Old UNIX was never really that beholden to standards. In practice, the de facto and sometimes "de jure" standards were just based on whatever was the most commo

Old UNIX was never really that beholden to standards. In practice, the de facto and sometimes "de jure" standards were just based on whatever was the most common variant of UNIX, which for a while was Solaris (it's oversimplifying, but POSIX is kind of like "standardized Solaris"), but is becoming GNU/Linux. Commercial unixes "based on" SysVR2/3/4 had plenty of "non-standard" behavior and extensions, it was how you differentiated your product. You support POSIX compatibility to enable portability if you need it, but you differentiate with your extensions or "weird behavior". GNU was no different. The BSDs just have their own tradition, one that's older than POSIX.