Yep GSM standardized on some of the Hayes AT commands and added many new AT commands. Considering GSM was published in 1990, that means they were working on it in the 1980s when these commands were regularly used. I imagine there's no strong incentive to update these commands and they keep getting migrated to whatever new voice and data protocol cellular systems tend to use when it comes to modem interfaces. I guess no one wants to sell an incompatible modem to OEMs, so these old AT commands will probably always be with us.
I remember seeing this a few years ago in some mifi device or something and thinking "Wait are those old modem commands?" I realized, well, that is a modem being used, so they probably just reused old protocols because why not?
List of commands for those interested: