In hindsight, that’s because high school calculus doesn’t teach you how things work and just teaches you a bag of tricks so you can grind through problems. There’s a certain number of tricks you should know, I.e., you should be able to take some simple integrals and derivatives, but for higher math, you run into complicated things where the tricks don’t work or don’t exist. Some of the tricks are actually really useful, but you have to fully internalize where they come from, e.g., integration by parts just comes from rearranging the chain rule, and, if you know that, you can apply it to more exotic derivatives.

I did well in HS calculus but struggled in college math because the bag of tricks approach doesn’t work there. It took a lot of effort for me to undo the bad habits I learned from K-12 math and learn the good stuff, but it paid off.

Also, it’s well known that eventually professional mathematicians hate certain kinds of math. There’s the classic divide between analysists (those that do calculus-type stuff) and algebrists (those that do things like group theory, and linear algebra goes here). You don’t have to like it all, and something you don’t appreciate the first time you see it, you may enjoy later