I agree that it is advantageous for companies to standardize but often they don't. React + Vue in one app might be a bit crazy but React in the main app and Vue in an internal app, or some secondary app might be OK. Resume-driven development is a thing, as well as joy-driven development. Devs are gonna be devs! There is a mild conflict between what is good for a devs career and what will make the shareholders of that company the most money. It is almost like a super-polite tug of war over future potential dollars between the two. Mostly incentives align but sometimes not.