That is most always the opposite of my experience WHEN said vanilla code is well written.
The problem is framework or no, bad code is bad code.
But think about part of what you said "every developer that knows that framework"
And that's a lot of the problem. People seem to learn the frameworks MORE than they do the underlying language, whilst in PRACTICE the framework should be something MORE to learn on top of JS.
Again that's why everything I've ever seen done client side with frameworks fits into one of three categories:
1) Things that would be less code and simpler to implement without the framework
2) Things that HTML and CSS should be handling
3) Stuff that has zero blasted business client-side if you give a damn about accessibility.
Taking a wild guess, the things you descibe? The UI thing is probably a mix of 1 and 2, and the first one you describe is probably a mix of 1 and 3.
But the way most people implement their JS and their UI's, it deludes them into THINKING the framework is somehow magically easier, or simpler.
It isn't. It's just that education in HTML, CSS, and JS are deficient.