OSS was not a widespread thing until much later, around the time of the early web and Linux. People were sharing code of course but trying to monetize development tools was perfectly reasonable at the time.

Licensing was in general messy and not very formalized (hence the existence of several BSD forks). There were may versions of unix, several of which were proprietary and built by various hardware companies (like Sun's Solaris).

Unix on PCs was even less of a thing at the time as PCs were still pretty limited. The 80386 with 32 bit instructions was only introduced in 1985. I'm not sure there ever was a unix version capable of running on 16 bit intel CPUs before that. So people programming for and using Unix hardware were mainly doing that professionally or in an academic setting and not on some home computer (as they were referred to once upon a time). So, companies donating OSS software was not a big thing.

Bill Joy of course worked on BSD kernels and distributions and would have technically been one of the early OSS developers. So, open sourcing vi was probably a natural thing for him when he created it in 1976 and released it along with the first version of BSD while at Berkeley. So, he was an academic at the time and not selling software for profit yet.