It's not marketing, is it. Unix, then Linux, won all the mindshare. No company is advertising Unix or Linux as better than Multics. Multics is culturally not a thing. It wasn't AT&T who dun it. It was Berkeley.
Doesn't have to be free to get mindshare, though it helps.
Multics lost the mindshare battle when Berkeley started distributing BSD. They would have had to go open source / free way back then, in 1978 or so.
Mindshare, mindshare, mindshare. That's the key for this sort of thing.
Oracle, for example, locked in SQL mindshare long ago. I'm not sure that Larry Ellison understands this -- after all, he (well, Safra Katz) killed OpenSolaris when that was a vehicle for gaining mindshare. But then again, maybe it was too late for Solaris anyways.
2. To mine it for ideas. I did this once with a different "old" OS that you never heard of. Found a cool feature, added it to Linux, and there's a fair chance you use it today. (details omitted to avoid self-dox)
