As best I can tell, C and C++ are the only languages where people are actually happy that there are multiple implementations.
The problem is when you have multiple implementations of languages that are effectively defined by their reference implementation, then the alternatives are usually an exercise in frustration.
Not to mention the terrible tooling to make multiple deployment targets possible (webpack, polyfills and whatnot)
Disclaimer : I'm still new and learning Java.
See the History section of https://en.wikipedia.org/wiki/OpenJDK?wprov=sfla1
On the other hand, I use gcc, clang, and MSVC++ on a regular basis. But... I think the reason I care about multiple C++ compilers is mostly because there’s no “one compiler that is ergonomic to use everywhere” and I end up writing better code because of it (eg gcc warning about something clang doesn’t care about).
For Python, I mostly just care that it Just Works everywhere (modulo compiler setup for building C modules)
I'm glad that pypy exists because it forces cpython to do something about performance, but for python overall it's a pretty niche tool.