[smacktoward]

Because they already know React, and they don't know Rails, Pug, Django, Laravel, et al. And using the skills they already have is easier than learning new ones. When all you have is a hammer, everything looks like a nail.

It's the same reason why Electron is so popular for desktop apps. On just about every measure, there's a better alternative available for that sort of thing -- native apps if you want speed and great integration with the host environment, Qt if you're willing to sacrifice on those fronts to get a single cross-platform solution. But Electron has one thing those alternatives don't, namely that if you're a Web developer you don't have to learn any new languages, toolkits, etc. to be productive with it. And it turns out that, for an awful lot of developers, "I don't have to learn anything new" beats just about every other consideration.