Much lower up-front costs. Actual delivery costs over the life of a fleet of satellites and a big enough customer base favors satellite delivery. Right now YTTV is losing money for Alphabet. It isn't enough for them to care about, and it is disrupting the industry, which is what they want, but if they had as many customers as AT&T or Comcast, they would care about how much it is losing them. Of course with all things Google, I am sure it is really about gather data to better target people with ads.
YTTV is just like any other startup company with growing pains and few customers at the beginning. They have kept it secret exact numbers so its all speculation on loses anyway. They just expanded nationwide so my guess that estimated 300k will soon be couple million.