Comment by chaimkut

Because in 3 years the frameworks, tools, etc. will have a much weaker base of developers than it its heyday (now). So in 3 years the framework will fall behind in browser compatibility, integration with newer tools, etc. Left to rot in the bit bin of history. And if I need to make changes in the web app, add new features, it'll be much more challenging if I also have to be dealing with framework maintenance in parallel.