It’s not so much that there’s no agreement, it’s that the different understandings all give the same empirical results, so there’s no way to decide on which understanding is “better”.
Settling the argument is a matter of taste, not science. At least for now.
That is a somewhat narrow definition of “why”, I’d say. But indeed, the transition from quantum mechanics to classical mechanics is unclear.
There are several interpretations of quantum mechanics, but they are empirically equivalent, so you can just pick your favourite and move on. That’s not necessarily a big mystery. The math works, as you say, and that’s the whole point of a physical theory.
There are also several interpretations of statistics. Does that mean we don’t understand “why” a dice rolls results with a certain frequency?
Note that superconductivity and the quantum Hall effect are both macroscopic quantum effects, so we do know what a macroscopic quantum system looks like.
Quantum mechanics is extremely logical - we understand the math extremely well, and the math describes reality better than any other theory.
It is, however, not intuitive.
Do you mean “why” as in “why did X cause Y” or as in “why are things the way they are”?
In the former case, quantum mechanics is our most precise theory for coupling causes and effects, predicting the outcome of experiments to an incredible degree.
In the latter case, do we really have a grasp of that for anything? Why is the gravitational constant the value that it is? Why is pi the ratio of a circle’s circumference and it’s diameter? Mostly we ultimately have to say that it is so because we can observe that it is so. For quantum mechanics it is the same.
Or do you mean “why” in some other way?
I’d say we understand quantum mechanics better than most things.
We know more about the behaviour of an electron than we know about the oceans, the Earth, the sun, the weather, the stock market, the human body, prime numbers, and so on.
What value does such an agreement have? Why is it a problem that there’s a plurality of equivalent understandings? Does that plurality add to or subtract from our understanding of reality?
You say the different interpretations give drastically different pictures of physical reality, but not in an empirical sense. But can we really talk of an empirically unavailable physical reality? If pilot waves, multiverses and wave function collapses all lead to the same empirical reality, does it make any difference to physical reality which one you think about?