Monocultures develop because of corporate backing. The web being open and unclaimed is what leads to the great diversity.
As someone who does both server and JavaScript development, the tools are not bad. Often times they solve real problems well.
The web's no longer an open platform. Yeah you can put up a blog on your own server using only FOSS. But if you want to drive traffic to it, you're using a huge corporate ad network or some SEO company. If you want to scale it, you're using a huge corporate cloud. If you want to make money on it, you're using a huge corporate ad network.