Many, if not most of the early public access systems ran some version of bsd UNIX because most of the universities had DEC PDP-11 or Vax, or Sun workstation hardware running a BSD derivative.
Wyvern, my own public access UNIX system, started as a back bedroom skunkworks project running on off the shelf PC class gear, and the only UNIX available for it was AT&Tish at the time. On the earliest systems, the only choices were Microsoft/SCO Xenix and Microport System V/AT, a new product that had a very attractive price point.
I chose Microport.