A reason the providers advertise on there own service is because people who don't have that service will see it when they go over to a place that has that provider.
For example, you have D* your family member has E*.  Your family member comes over to watch a baseball game.  You both sit down and turn on D*.  During a commercial D* advertises MLB Extra Inning.  Your family member might become interested in switching to D* because he is a baseball fan, and he would like to follow his favorite team.  He can't do that with E*.  The EI commercial will state how someone can follow their team all season long.  It will also give the introduction promo price for a new subscriber.  And you tell them if he switches over, you can do the $100 refer a friend if he does switch.
D* gets a new subscriber, both of you get the $100 refer a friend credit, just because he went over to your place to watch a ball game. That is why the providers advertise on their own service.
The Aflac commercials with the duck are entertaining.
