I'm not so sure about that. The great thing about software before SaaS (as a business model) was that selling another copy was basically zero marginal cost. And of course there were the extremely lucrative "professional services" you could reap because installing an enterprise software package on-prem was a nightmare.

Maybe it's just that the open source ecosystem covers most of the low-hanging fruit for things that could be libraries. And things that are big and complicated and require their own databases and such are easier to run as services for the actual user.