Ask HN: Why so many JavaScript frameworks?
Because organizations with specific needs and significant resources often benefit from writing their own framework to exactly fit their use case. Consider Facebook, to a first approximation, there is only one framework. Google is in a similar position, though there may be more than one framework, there are not many frameworks.
For organizations without significant resources, JavaScript frameworks can be a bit like wearing someone else's underwear. Technically it works, but you're probably looking for a better alternative.
Nothing wrong with having many choices but to answer the question I think it's because of the sheer of popularity it has. I mean it is the language of the web after all.
If you know how to program but not what to program, creating a framework is just about all you can do.
I bet majority of frameworks are built for a certain project/need. At least mine are (RE:DOM for example, https://www.redom.js.org).