At BYU faculty are supposed to either publish their textbooks with reputable national publishers, or through BYU publishing.

If they're self-publishing, or using a "custom" or on-demand publisher (even if the custom publisher is owned by a major publishing house) then they may be charging more for their books than BYU would deem appropriate.

I'm not saying this guarantees cheap books. But it's supposed to limit the old professor's trick of charging you $100 for the textbook they couldn't get published by a real publisher but are requiring you to buy for their class anyway. (Which I believe is far less common at BYU these days, and was probably never as common as it is at many universities.)