I think these languages are thriving in the cloud because they not only have a favored concurrency model, they have it mandatorily and so they spun a cohesive ecosystem.

Take Java for example. You can make an event loop and use it on a web server (Play framework is just that). It doesn't mean you can retrofit all dependencies to do the same. It also doesn't mean business logic inside this server will necessarily use one instead of spinning up os threads nor that it can even plug into the same event loop. And it also means you just introduced opposing views into your ecosystem.