The real reason is the industry. We don’t reward deep knowledge of a particular language anymore. Things change too quickly.

Imagine a really good Angular dev who’s been using it for 7+ years. Sure, their code might be fast, but everything’s moving to React now.

Even backend languages change quite a bit. .NET Core is a big winner in performance compared to .NET Framework, but you can still write lousy-performing code in it.

From an architecture perspective, people seem to have a hard-on for serverless lately. Which typically involves considerably more HTTP requests, which causes performance issues. On a simple test system things are fast enough, but once you scale the latency starts to add up.