I probably had crummy teachers in some places, but my experience was that math up through linear algebra made sense and wasn’t all that bad, but that calculus was a huge bag of “if it looks kinda like this try this thing, and if the result looks kinda right it probably worked, if not try this other thing” such that I could never form a framework for it in my head. Also didn’t help when teachers in some things would say “oh this is much easier and more straightforward with calculus”, even without a prerequisite for it, and proceed to only explain concepts with calculus half or more of the class had never learned. One of these days I need to find a way to get it the right way.