std::println dates to C++23. This is very recent. You only have to be using Clang 18 (March 2024) or older to find the feature unsupported: https://godbolt.org/z/xPqYafhss (Clang 19 dates to September 2024, only a year ago.)

In contrast, the standard C++ stream types have used operator<< overloading for more than 25 years. glog/gtest assertions continue to use it.

I said "these days"... C++ is an evolving language. And while it doesn't throw things away, it does collect enough "stuff" that you can choose to write nicer and more straightforward code than before.