Earlier quoted context omitted.
I think it's more about having a stable interface. If it's not stable - you can't use it as a base tool long term. But if it's stable, what difference does it make if it's POSIX compliant or not?
Because you aren’t the first one here. Countless lines of software exist which assumes posix. People learned how to use computers and know the grep commands. There is documentation for posix in places where it needs to be. It handles important edge cases which were needed by some groups and that was formalized into a standards requirement. So changing to the new thing invalidates all that existing value. That’s not a…
Example: https://github.com/mpv-player/mpv/commit/1e70e82baa91
Anyway, I don't see any of that as a reason for not having ripgrep installed everywhere by default and as an argument for not using it.