It depends on what kind of websites are you talking about. If it is more of a web application with heavy interactions on the page, you are probably better off using a js framework or you will end up writing your own in some ways. But if you are talking about web pages with javascript to do a few fetches here and there, you can surely use vanilla js.

So as a developer, no I am not using vanilla js to answer your question because I work with interaction heavy web apps where I am better off with a well tested js framework. I don't have time (time is money) to try and do those interactions using plain js (I at least suck at plain js). One anecdote for you.