> I understand that people can have many things to say about C++, and I do as well, but `std::span` should have been there decades ago (...)

Decades is kind of a stretch. C++11 introduced smart pointers, and finally getting C++0x out of the door was already a major victory. Given the history of C++, it would be unrealistic to introduce something like std::span before C++17.

Meantime, some organizations are still struggling to migrate to something like C++14.