If you're a small team or a solo dev working on a simple app, and you know the source code very well, frameworks might not be the best choice.
However, if you've ever worked on a team of revolving contributors, constantly shifting requirements, or have any reason to reuse code across apps/repos, frameworks help immensely.
The biggest benefit to using something like React imo, is that when we hire somebody familiar with React, they can hit the ground running and start contributing immediately. Unless your app is dead simple, you won't be able to have the same velocity in a homespun framework (and given enough time, most "vanilla" apps turn into homespun frameworks).