blocked commercials

What gives AT&T tv/Direct tv the right to block commercials during network tv shows?  I've seen it during my nightly news (nbc) and during many shows on several channels.  Usually, it's maybe 30 sec commercial once or twice during a show.  Today it occurred a doz times during the 1st half of a college football game; some went well over a minute.  It's my understanding ad buyers pay either show producers or networks for ad time.  As a former Comcast tv subscriber, I remember many AT&T commercials that comcast had running during the many shows/games carried on their cable.  I should think it would have been improper for them to do anything to block those.  It's none of their business.  

Now, I see these freeze screens w/music called `commercial break' and can only guess it's a comcast commercial that they've paid for and is being carried on Hulu, Roku, Charter, and others maybe except AT&T.  I hope someone can enlighten me as to how AT&T get's away with this.  As a paying subscribers to AT&T I might feel like I'm being denied, though I've felt too many commercial breaks in too many shows today.  this has been going on since I started 6 months ago.