When you put it that way - yes it is odd.

From a general business point of view, they are promoting a page and social media seems to be the way to go about this. How best to promote their own page but through the employees, who tell their friends who tell their friends etc etc? They have to start somewhere.

In your case, I think it is odd that they would make a big deal of banning FB etc then ask you to "like" them. lol! I certainly wouldn't feel obligated to "like" their page, given their attitude & lack of trust in their employees.