...It should be impossible to discover why... There should be some...
How could you possibly know this? Nice conjecture, but that is all it is.
My reasoning was in the next sentence. It follows from the definition of fundamental. To avoid infinite regress, you need something, some foundation, that's not caused by anything else, and by definition that something will be impossible to explain because it is not a result of something to be explained. You would no doubt have some kind of explanation for it, but it would be an unprovable conjecture at best. You can't prove the axioms.
We presently have a set of fundamental laws in physics. If any of them are really fundamental for the universe, you wouldn't be able to break them or combine them into simpler and/or fewer components that they step on. There would still be one obvious explanation that's quite popular nowadays – there are an infinite set of universes, and each set of fundamental laws you can imagine exists somewhere, and our laws are a result of some sort of cosmic darwinism (universes without sentient lifeforms would not observe themselves into existence). If you can't travel between these purely hypothetical universes though, you'd be stuck with exactly this kind of unprovable conjecture. If you can, you'd end up with a new set of fundamental laws of the multiverse that govern your ability to travel between them and the same problem, and a different kind of unprovable conjecture.
There's one more option though: All roads lead to us. That is, any possible universe would develop sentient life that's comparable to us at some stage, and whatever fundamentals there are, they would be just randomness that does not need an explanation. Which would be another conjecture that you can't prove without an exhaustive search in all possible universes.