What does Preview do that's hard to match?

Genuine question. I've been a Mac user for decades and on balance think it's quite good, but Preview is one of the most deeply frustrating, buggy, and unintuitive pieces of software on the system--it's at the top of the list of things that I wish I could swap out for something--anything, MS paint would be fine--else that was as deeply integrated in Finder/image/PDF interactions.