React / Angular JS etc tend to require spending a lot of time learning how it works first. Then you have to build almost all your application around it. This can take a lot of time, which pushed up costs and complexity. If you are building something like Google Docs or Google Maps you want to build it like a SPA. For a lot of the sites I've worked on in the past building it as a SPA was completely unnecessary.

> react is doing what php did a while ago (and is still doing). it's mixing frontend with backend stuff. i personally find it refreshing!

We've been trying to get away from that for quite a while. I try to write almost all my JavaScript in a way that assumes as little as possible about the page structure, the web application etc. It can be done, however it requires thinking about how your markup works and how the page works.

Generally you should have good separation between your markup, your styling and your scripts.

> we did that for a while then people came and told us how bad it was and we needed to do strict MVC or whatnot. now everybody is doing it and it's cool again!

The problem is that it is cool again. I don't want my backend code tied to my front end code.