Except that many profs write their own textbooks and then market them to a captive audience. I had a chemistry professor in undergrad who had the #1 textbook for the 101/102 level courses. He was a super nice guy, but one could not overlook the business angle there. He saw a niche and filled it with something of very high quality.
We have to keep in mind that not every professor is independently wealthy, in fact, most are not. If they can find success marketing their textbooks, they should. Where I draw the line is the insidious behavior of the publishers. Often the authors are as big a victims as the students.
So all I ask is that you "everything free" types keep in mind that people should be paid for their hard work. That it doesn't automatically mean someone else is being exploited and it certainly doesn't mean that the result can't still be open source. I am highly skeptical that anything high quality and worthwhile will come from uncompensated authors, editors, and publishers. Nothing ever works like that.
And yes, I was in higher ed as an undergrad and graduate student 2x and then as a professor for awhile. I have seen the best and worst of higher ed.