inflight wifi doesnt work on AA

It's crazy I'm on the same plane 2 flights in a row the first flight Tmobile access was there. The 2nd flight it was replaced with "watch this ad video for 20 min free wifi" Why does Tmobile allow that? And why do they advertise wifi if it's selectively not going to work? There is no way to know if it's going to work until after take off and it's been happening a lot during the holidays. Sounds like someone is being greedy.