If you provide an end result response from your web app to a user's browser in 50ms-100ms (before external latency) then things like 200 microseconds vs 4 milliseconds have less of a meaningful difference. If your app makes a couple of internal service calls (over HTTP inside of the same Kubernetes cluster) it's not breaking the bank in terms of performance even if you're using "slow" frameworks like Rails and get a few million requests a month.

I'm not defending microservices and using Kubernetes for everything but I could see how people don't end up choosing raw performance over everything. Personally my preference is to keep things as a monolith until you can't and in a lot of cases the time never comes to break it up for a large class of web apps. I also really like the idea of getting performance wins when I can (creating good indexes, caching as needed, going the extra mile to ensure a hot code path is efficient, generally avoiding slow things when I have a hunch it'll be slow, etc.) but I wouldn't choose a different language based only on execution speed for most of the web apps I build.