Would you mind elaborating? React[1][2], Angluar[3], and jQuery[4] all started as personal projects to abstract architecture for use by other people. These things started in an age of JavaScript years before TypeScript was imagined when writing large expansive architectures in JavaScript was a real risk. Full stack was not a thing yet and IE was still very real. However, most developers at the time were not writing large applications, at least not in this language. The primary concern for most developers was make things easy. I remember this was the intended selling point of AngularJS (first version) and it looked like garbage for Java developers.

[1] https://blog.risingstack.com/the-history-of-react-js-on-a-ti...

[2] https://medium.com/@sjarancio/reactjs-a-brief-history-3c1e96...

[3] https://medium.com/the-startup-lab-blog/the-history-of-angul...

[4] https://medium.com/@andrewchall92/how-jquery-was-born-a-brie...

Now if you have written your own applications nearly 60-80% of it executes outside the browser even when the only interface and use case is in the browser. The current common use case for these frameworks is that most developers cannot write original software and when they try they either fail, with plenty of face-saving excuses, or just create something that looks identical to their favorite framework. This is the primary problem these frameworks currently exist to solve for.