Actually you got it wrong, it was precisely because AT&T could not legally charge the prices other vendors were selling their OSes, that UNIX got adopted by universities and small business, thus spreading its use in the industry.
The ones charging lots of money for UNIX clones were Sun, HP, Digital, HP, ...
I do remember, um, liberating an overlooked copy of system V/386 on 5.25" floppies that I found in a storage cupboard when I worked at PC Magazine in 1992 :-)
"A Narrative History of BSD by Dr. Kirk McKusick"
https://www.youtube.com/watch?v=ds77e3aO9nA
"Unix came into many CS departments largely because it was the only powerful interactive system that could run on the sort of hardware (PDP-11s) that universities could afford in the mid '70s. In addition, Unix itself was also very inexpensive. Since source code was provided, it was a system that could be shaped to the requirements of a particular installation."
Or as a famous talk once said: fuck you, pay me.
In a way OSS seems like the sort of thing that would have worked great in some hypothetical enlightened communist system that didn't suppress liberty.