POSIX isn't very relevant, but the set of basic Linux tools with generally expected features and behaviour is. The difference is that the latter evolves. For ex

POSIX isn't very relevant, but the set of basic Linux tools with generally expected features and behaviour is. The difference is that the latter evolves. For example, when GNU tools appeared, people started to prefer them to POSIX tools, because the GNU tools had useful extensions. POSIX never catched up. So we have seen more friendlier set of tools than POSIX would force on us, but it was evolution, not revolution. Why, maybe because people see value in continuity and acquired knowledge and don't want to start using obscure new tools like ag or exa, even if they could be superior.