As I began to learn web site creation, I often heard statements like "vanilla JavaScript is only for beginners". As I began to learn JS I certainly mainly stuck to vanilla, fulfilling the stereotype. Frameworks were mysterious and confusing concepts.
But, crucially, I work for a consultancy not a software company. They are interested in three things:
1. Getting an effective app
2. Maintainability
3. Maintainability
It is of no value to have an app that no one else in the company can update or that require outside skills that are too specific. We can't hire someone so tightly bound to a technology, it is too restricting and not future-proof.
So vanilla JS is great for making effective (adequate) apps, useful for training others in the company and if we need outside support then we aren't restricted.
Plus the same (more-or-less) vanilla JS and any packages will always (??) work in various different scenarios: web front-end, mobile, NodeJS, Chrome extensions, Electron etc. and with fewer version compatibility worries.
Now, if we wanted to build a huge and complex multi-engineer project then a framework might be necessary - but if so we'd likely hire a specialist agency to do that. Which of course means we lose control of the app... Not so attractive!
"Vanilla JavaScript" is just the basics of the language, and learning some of the more advanced abilities. Frameworks, libraries, etc. all build on the basics. You don't need to know everything, but it helps to understand how JS works behind the scenes.