Georgia Tech has/had its own publishing company. They actually encouraged their faculty to write books like this. I can't seem to find any information about it, but I swear it was there when I took classes in the late 1990s.

BMED2013 and it was still the same in my years. The culture has shifted a bit amongst professors though. After sophomore level classes I remember that professors will often just email you their textbook if you asked (a lot of times they’ll offer to “work it out”with you if you can’t afford the textbook).