> CS101 basics (appending to an array?)

Probably because most professionals are not fresh out of CS101 & most data structures aren't arrays or exposed as arrays.

List, Collections, Map, Trees, home-rolled data structures better suited to domain - how do you not get this?

Your opinion sounds like that of someone just out of a bootcamp. You're putting all the weight on irrelevant syntax issues. A lot of devs use multiple languages day to day amongst other things.