Then students will just end up paying more in tuition, possibly more than the costs of textbooks. That extra money of course will go to increasing either/both the university president's or lead football coach's salaries.
The colleges will raise tuition anyways, and they do it at a runaway cost. Might as well throw in something useful and tangible like textbooks that they can bargain wholesale with the publishers. Individually, the students can only beg.