I don't get a lot of opportunities to play around with JS frameworks, which is odd because I hobby-code a lot in JS. I imagine the top reasons to use frameworks are cross-browser compatibility and support for scalability in the domain of your work. Unfortunately sometimes people use them because the only tool they have is a hammer, so everything is a nail. Vanilla DOM manipulation has become much easier in the past few years. I have played around with some new DOM features in my own time, but for anything public-facing I'm going to use a library that allows for cross-browser compatibility, and typically that's a combination of jQuery, polyfills, etc.