BTW Josh, I am trying to be respectful here. I suspect you are tad younger I am and your early introduction into UNIX was on the WINTEL platform, not on the DEC systems like mine. So, if I'm going to make a guess you were not in a position when you were introduced to be able to get access to the sources.
So in your experience the UNIX source were closed to you personally (and many others). I get that. But it does not change the fact it, there were available and there open and were not a secret. Which was very different from many of "closed" systems (says Cisco, or much of the other infrastructure) of the day. They always have been. Even System V.
It was quite easy to get source if you were willing (and could pay). I'm not suggesting that it was easy for you could and I understand that frustration. I personally would not have been able to pay for the licenses, but I was being employed by firms that could and valued my abilities, so they did. This was also true for many educational institutions.
Sun and DEC actually were quite liberal with their source licenses, because AT&T had been. They had to be also - because their customer required it.
The point is there is a difference between "open" and "free." There are a lot of things that are open and we can look at but not touch or have the wearwithall to modify. But that does not change their openness - we can still (and do) learn from them.
Linus and many of us learned because UNIX (the ideas) and the basic implementations were open. We talked about them, they were well specified. We wrote application that relied on those ideas, APIs etc. And Linus, Andy Tannenbaum and Plaguer before them reimplemented those ideas and created clones. Unix was and is "open" and the implementations were and are available. The problem for many is the price to look at the implementations - that I grant. And for many, for some of those implementations, can be high. But it does not make them "closed."
The effect may seem that way to you, but it was not and is not the same. All, I'm asking you to say, is that traditional UNIX implementations such as System V were not "Free and Open," unlike Linux some of the other Unix clones. And that make all the difference.
They were and still are open.