I’ve been learning piano for over a year gradually learning more and more pieces like that, and I’m starting to notice a limit to memory. The basic melody is easy to remember as you point out, but piano music often has multiple things going on at once, and it gets harder to keep track of all that in your head.
The best piano players in the world play by memory whole concerts evenings with incredible complex and hard to remember music like JS Bach. They play hundreds such of gigs a year reliable with a very big repertoire.
