Why don't professors start companies? Why don't more professors attempt to use the knowledge gained during the course of their research work by starting a company and commercializing their findings?
I'm asking this question per this comment.
This question seems to be based on a misconception, namely that professors start companies substantially less frequently than they could or should.

The vast majority of professors, even in fairly applied areas like computer science (compared with literature, say), are simply not in a position to start companies based on their research.  You need a viable business plan, and they don't grow on trees.  Specifically, even really profound research with many practical applications usually just doesn't have obvious commercial potential as a stand-alone business, since it won't be clear how to monetize it.  Of course, there are exceptions, and plenty of important businesses were started by faculty, but only a small fraction of professors could do this successfully.

Here's another way of looking at it.  There's no reason why a business based on a professor's research needs to be founded by the professor.  If you see someone with great ideas, you can buy the rights to the ideas and found your own company.  If professors were missing a lot of wonderful opportunities to found companies, then you'd expect entrepreneurs to step in and do it, but that doesn't happen very often either.

Ultimately, this is why we have academic research.  The stuff that leads to obvious business plans could easily be funded by industry.  By contrast, one of the reasons why academia includes research is to make sure work that can't easily be sold doesn't get neglected.