The Standard Model of Particle physics sets forth a huge range of possible phenomena and interactions. But, most of them are observable only in high energy collider experiments recreating circumstances that have not existed naturally in the near vicinity of Earth or the Sun for many billions of years, certainly, long before life as we know it came into being.
Why do we have such a sophisticated set of parts and rules for such a simple universe that makes so little use of so many of those parts and rules?
There are six kinds of quarks: top, bottom, charm, strange, down and up (in order of mass). But, all ordinary matter made up of quarks is made up of up and down quarks, with an occasional strange quark flitting into and out of existence in a kaon within an atomic nucleus. Gluons and quarks are also always confined within hadrons at temperatures cool enough to come into being on Earth or in the Sun, so we never see them in isolation. There are hundreds of possible mesons and hadrons (even before venturing into tetraquarks, pentaquarks, and hexaquarks), but protons and neutrons and several mesons with no significant strange quark or heavy quark components (i.e. the pion, the omega meson, the rho meson and the sigma meson) that are involved in the nuclear force, suffice to describe almost everything in the observable world to a high degree of accuracy.
Apart from nuclear physics, which only has a narrow range of engineering and scientific applications (apart from understanding fundamental physics for fundamental physics' sake), we don't need to know anything about the strong and weak nuclear forces at all, beyond the fact that nuclei hold together in the absence nuclear fission, nuclear fusion and radioactive decay which could be described with far simpler phenomenological models (and as a practical matter are dealt with that way, even today, in most engineering applications). Nuclear weapons, nuclear fission reactors and the early forms of nuclear medicine were invented as practical applications of nuclear physics before QCD or electroweak theory had reached their modern Standard Model form.
We know that there are three kinds of neutrinos, and three kinds of anti-neutrinos, and some of the rather mysterious properties like neutrino oscillation, but they interact so weakly that there aren't many applications in which knowledge of them is helpful, and there are even fewer applications in which it is necessary, possible and helpful to distinguish between neutrino flavors.
We know that there are two kinds of particles (muons and tau leptons) that are just like electrons but more massive, and how they behave, and we even use muons in a number of practical applications.
But, in a universe with twelve kinds of fundamental fermions, most of what we observe can be understood with just three of them (up quarks, down quarks and electrons), throwing in the electron neutrinos, muon neutrinos and muons and bringing the total to six, for the truly sophisticated. A world without second and third generation fermions at all would be almost impossible for a casual observer to distinguish from our own.
We live in a universe with twelve or thirteen kinds of fundamental fermions, but the eight kinds of gluons are always confined, the Z boson has negligible relevance practically, the W+ and W- boson can be summed up in a black box theory of weak force decay for most practical purposes, and the photon and possibly the hypothetical graviton, are all that we need to deal with for most purposes.
One needs to understand special relativity for many practical purposes, but the far more mathematically and conceptually difficult general relativity for far fewer. We need to understand quantum electrodynamics for many practical applications, but electroweak theory and quantum chromodynamics, for only a very few applications.
We know all of the fundamental physics that will ever be necessary to understand chemistry and biology and geology from first principles.
We understand the least about gravity, but fortunately, while knowing more about it is important in terms of cosmology, and explaining what astronomers see in the very distant depths of the universe, none of the mysteries of dark matter and dark energy have any practical relevance to a species that may never settle more than a handful of nearby star systems, a scale too small for either of those phenomena to have any real relevance. For all but the highest precision applications, even in the solar system and its nearby neighboring star systems, plain old Newtonian gravity and special relativity are quite sufficient to meet our needs.
And, I think that we will probably master the main problems of quantum gravity, dark matter and dark energy, if not in my lifetime (not an unlikely possibility if I live to a ripe old age), in the lifetime of my children or grandchildren (assuming that I will have any). Knowing this won't have many applications, but it will be satisfying and I suspect it will overhaul a lot of mainstream astrophysics related to conventional wisdom about cosmological inflation, the early universe, dark matter and dark energy, in a way that may leave some philosophical ripples that escape into the larger culture.
Cracking the unsolved problems of high energy physics is something we crave, and we might someday discover a layer beneath what we know now that explains Standard Model physics in terms of something simpler at a more microscopic level that unifies it and provides a means from which its many arbitrary constants can be derived from first principles. But, it increasingly looks as if there is no beyond the Standard Model physics that would make differing predictions from the Standard Model in any way that matters.
I am skeptical that we will penetrate that deeper level any time in the next several centuries, no matter how many billions of dollars of resources we throw at it, and I am even more skeptical that we will be able to find any technological applications for it if we do. Understanding the deeper underpinnings of the Standard Model, or at least some of them, will probably only satisfy our intellectual curiosity and make our knowledge of a few physical constants that could then be calculated from first principles. a few orders of magnitude more precise that what we measured experimentally something that is already quite precise in most cases.
Really the only bright spots in terms of progress for the next few centuries in Standard Model physics are an improved understanding of neutrinos, increasingly accurately measured fundamental physical constants, and an increased ability to apply QCD to high energy physics experiments, neutron star properties and the Big Bang.
Much of what we know already is only applicable to the early moments of the universe right after the Big Bang and has little application once nucleosynthesis has run its course.
While we have not yet reached the point of complete scientific knowledge, our understanding of fundamental physics is such that we already know almost everything that could have a technological application that would be economically useful in any way.
We know such more beyond what is economically or technologically useful already, and yet, this knowledge is already esoteric to a great extent.
Now, this doesn't mean that just because we know all of the fundamental rules of physics that we need to use, all of the laws of nature that matter to us, that there isn't lots of critical and economically valuable science to be done, explaining all of the implications of those fundamental rules that are relevant to our complicated world. In areas like condensed matter physics, nuclear engineering, genetics and medicine, there is much to be learned. But, you can go a long way towards doing that with QED and practical simplifications of those fundamental rules for circumstances were they need to be applied and experimental measurements more precise than those that could be derived from first principles.