I recently taught a course on ODEs, and it took far more than "a few hours" to curate enough online resources to cover the curriculum. The sad truth is once you get out of calculus, the number of quality online resources for advanced mathematics decays rapidly, and the coverage gets spotty as well.
This is not to mention that those resources rarely agree on notation, which makes them more confusing to students (and therefore less helpful). There's something to be said for requiring a single edition of a single textbook, just for consistency's sake, even though that's caused all this publisher drama in the first place.
This doesn't require any explanation other than inertia.
> No USF employee may receive any money in exchange for requiring a textbook. However, if the professor is the author, royalty payments may be received.
It references and quotes Florida Statutes 1004.085. "An employee may receive: ... Royalties or other compensation from sales of textbooks that include the instructor’s own writing or work."
Just in case you don't think FSU or USF are reputable, I found http://www.thecrimson.com/article/1985/10/4/sandel-donates-b... from Harvard, back in 1985:
> Harvard has no policy on whether professors can profit on the sale of texts to students in their classes. The University leaves that decision to the individual instructor, according to faculty officials.
or more recently (Harvard, 2008) http://www.thecrimson.com/article/2008/3/4/professors-find-d... :
> Since N. Gregory Mankiw returned to Harvard to teach the College’s introductory economics class, 2,278 students have filled his weekly lectures, many picking up the former Bush advisor’s best-selling textbook, “Principle of Economics” along the way. ... So, what has professor of economics Mankiw done with those profits? ... “I don’t talk about personal finances,” Mankiw said, adding that he has never considered giving the proceeds to charity.
Given that Florida law doesn't prohibit collecting royalties and that a Florida school and a Massachusetts school both allow collecting royalties from assigning one's own text books for class, I think the burden of proof is on you to show that "most reputable universities don't let you do that."
(In any case, I went to university about 20 years ago, and the laws and rules were different than. But it doesn't look like it's changed all that much.)