They are also constrained languages which gives many advantages. POSIX regex will always execute in O(n), Perl "regex" are potentially exponential and can be a security risk in certain situations.
Well, that's at least an actual argument, even though POSIX regex would have never proven so useful in a variety of use cases.
Other than that, I'm completely shocked that somebody would praise sed or awk in well into the 21st century. Turing-complete languages barely capable of properly solving any problem that has any sort of algorithmic complexity, let alone one that requires proper data types, variables or interacting with any sort of system. Really, you can do that in Perl (even in Raku) without your couple-of-liner horribly breaking down once you need some custom logic to it. Oh, and it will even resemble programming languages, not some hieroglyphs left behind by aliens.