You don't get hired for, say, a role that requires Svelte / React expertise by pointing out "I did it in vanilla JS!" - so you are correct, industry sets the rules and your CV if you want a job from them, needs to reflect this.

There are also software engineering (not programming) reasons, mostly because they set standards for stuff like state management, for why they're useful - helps with future maintenance, documentation etc. when you don't have to interpret a custom self-made framework and teach it to hires.