This is actually the biggest head scratcher of AT&T's video strategy. With DISH and Sling it makes sense because they are targeting different markets and different contractual obligations around the channels they carry. But with AT&T, they actively wanted to consider U-Verse, DirecTV, and Stream to be the same service so that they get more favorable rates from programmers
It's kind of silly that a U-Verse or DirecTV satellite subscriber can't just log into DirecTV Stream. Today, it makes even less sense because now DirecTV markets them as the same service just a different delivery method, which is even more integrated than it was during the AT&T days