Regarding the "Flavor" question:
Almost certainly the biggest fatal flaw preventing UNIX from getting any serious foothold in the market during the 1980s was licensing. UNIX had such a convoluted history it was really unclear at the time who deserved to be paid for it, and just how much. Unix was "invented" at Bell Laboratories (AT&T) at a time when AT&T was a government-blessed monopoly... they were "the phone company" in about the same sense that the "post office" still is today. Because of their unique position there were a number of consent degrees in place that dictated exactly what sort of products AT&T could sell "commercially". UNIX fell outside of that, so despite being owned by Bell laboratories and technically costing something like $40,000 for a full license it was essentially a non-profit exercise, and its wide distribution at universities and the loose (nearly nonexistent) enforcement of the licensing agreements made it essentially "open source". However, in 1983 when the government finally broke up AT&T's phone monopoly the company was no longer constrained by the consent degree and was technically free to sell UNIX as a product. And thanks to that UNIX development went to heck in a handbasket.Here's an article talking about what happened. Look at the 1980-1990 section.
"BSD" is sort of a red herring here, because despite being "different" from AT&T's System V commercial product there were still legal issues with it. At the time BSD was technically packaged as a set of changes to an original Bell Labs source port... to be squeaky-clean legally you still needed to have an AT&T source license to work with it. In the late 1980's active efforts were organized to clean out the licensed code and replace it with "free" versions, but it wasn't until 1993 that BSD was indisputably available as a full stand-alone operating system without any AT&T encumbrances
. Sure, by the 90's if you were developing a proprietary UNIX you'd almost certainly be better off going with BSD's source than AT&T's if for no other reason then you could simply download it all for free, slam the door, and just note that you used it in the footnotes of the user's manual. But in the 1980's there were legal landmines scattered all over it.
As to why so many computer vendors had this strange obsession with producing one-off UNIX versions in the 1980's... well, in retrospect it does look pretty silly. There certainly was a desire in academia for UNIX boxes then, and the pricing of the systems being used to provide it were stratospheric despite the hardware not being that much more powerful then the state-of-the-art in home computers by the middle 1980s. If adding UNIX could turn your $3500 home/business computer into a "workstation" which then could be sold as a replacement for a $10,000 SUN then the math must totally make sense, right? Even with the overhead of a UNIX license and associated development costs?
Of course, it never did actually work out, but the theory was probably sound on some level.