“That’s just how it is” usually means nobody bothered to ask.

Most arrangements that feel permanent were decided by somebody, for reasons that may no longer exist. The phrase is not usually a lie. It is an honest report that nobody in the room knows the reason, which is a very different thing from there being a good one. Whole systems run for decades on an answer nobody has checked.

When you hear it, ask who decided and when, in a tone of interest rather than challenge. Half the time the answer is an old constraint that has since disappeared. The other half you learn something real about why the thing works as it does.