Professors don't tend to be very good programmers themselves, because they're often tied up in the science aspect of "computer science" or, of course, in teaching.

You need to practice programming to keep the patterns in your mind and to try out new libraries/technologies.
In particular, software architecture can only really be learned by building (multiple) large applications from scratch. That ties you up full-time for years, which you have time for, if you're a full-time software engineer, but not as a professor.