One problem is that more and more, people expect the browsing experience to include a lot of responsive features that require a bunch of client-side JavaScript.

Except JavaScript blows, the emerging JS extension ecosystem that tries to fix that is still highly in flux (and mostly blows), so developers try to keep their server-side stuff NOT JavaScript, and then supporting server-side rendering means re-implementing everything twice.

Of course, this doesn't excuse document-centric sites like news and blogs.