Not so sure. I learned commercial Unix back in the late 1990s on discarded SPARC hardware which was available in skips and Yahoo auctions for virtually no money at all. In fact it was generally cheaper than the boxed Linux distributions you had to spend on because you only had a dialup.
The killer with the commercial Unixes is that the documentation was orders of magnitude better. That is true today still as well. Most Linux knowledge I have to sift through today is obtained from dubious quality manpages, partially incomplete or out of date documentation and random blog posts.
I'm not sure free/cheap Unix workstations are a ubiquitous experience (indeed I don't think I've ever seen a skipped working Unix box!) Late 90's was good for SPARCs but I spent a load of time looking out for AIX kit and it was seriously hard to come by, without spending a lot of money.
Also, even if that works for individual hobbyists, it doesn't scale to things like University courses. There having Linux means it's easy and cheap to teach unix-like setups. Whilst top-end universities might be able to kit out labs with Unix workstations, it's been much cheaper to setup labs with PCs and Linux for a long time.
So Universities will churn out thousands of people familiar with Linux tooling every year, leading to easier hiring leading to more companies adopting Linux.
The killer with the commercial Unixes is that the documentation was orders of magnitude better. That is true today still as well. Most Linux knowledge I have to sift through today is obtained from dubious quality manpages, partially incomplete or out of date documentation and random blog posts.