Do colleges/professors sign contracts with educational publishers?

I am attending a community college in the US, and one of my professors has made it a requirement to purchase a login from McGraw-Hill Connect, even though our school is already set up with a decent online-learning platform. (This is a traditional class, by the way - not an online class.)

So far, the only material that has been placed on this McGraw-Hill platform (which I paid $120 for) is a weekly multiple choice homework assignment which could easily be handed out on a piece of paper or distributed via the previously-mentioned platform (which is already available to students taking the class and requires no additional charge).

What would be the incentive for a professor to require students to purchase this "extra feature" which, for my class, provides little-to-no real use and reaps in thousands of extra dollars for McGraw Hill? Is it possible that my professor is required to do this to fulfill some sort of contract?