So you say "It's the publishers" but you haven't really explained the mechanism of action?

Who writes the class syllabus? Nobody from the publishers does, professors and or departments do that. Maybe based on advice from collage admin. But it is all in-house. Ultimately the college picks the books, they're the gatekeepers.

Calling it "inertia" feels very dismissive; and isn't close to an explanation of why somehow Higher Ed Professionals share no responsibility.