Apple and Google focusing on their own stuff, is one of the reasons why clang lost velocity in ISO C++ adoption, most of the C++ compiler vendors that fork clang don't contribute frontend stuff only LLVM, and with them out, it took some time until new folks jumped in to replace their contributions.

Likewise you will noticed MSVC is no longer riding the wave in regards to C++23, after being the first to fully support C++20.

Then there are all those other compilers out there, lost somewhere between C++14 and C++17, and most likely never moving beyond that.