Do colleges/professors sign contracts with educational publishers that require them to use the publisher's learning platform? 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?
Is it possible? I suppose so, but that's not the way things normally work. Usually the professor, or a committee of professors, decides what textbook and/or homework system to use. There is not usually a contract, and they can change to a different book or system at any time.

I can think of several more likely reasons for using the system:


Simplicity. A generic online learning system like Blackboard has little pre-made content, while a system from a publisher will come with questions already written.  Writing even one quiz per week "from scratch" in Blackboard is highly time consuming. Giving quizzes on paper is also more time consuming, and takes class time. 
Textbook integration. The online systems from publishers are often tightly integrated with an online textbook. Students often complain about systems like Blackboard, saying they don't see the link between the questions there and the textbook.
A desire to try out online systems. From the question, it sounds like the professor could get more "value" from the system. Perhaps she's just trying it out, before really committing to it. Or perhaps she is concerned about complaints if she assigns more frequent assignments. Student feedback is important in this case. 
If a committee decided that the online system is required, perhaps the professor could be "playing along" by assigning a minimal amount of work on it, just enough to avoid criticism from colleagues.