HDMI
Now imagine all the issues.
Tons of customers would demand free HD installs to their TV2. "You're trying to tell me that you sold be a box that runs 2 TVs in HD, but won't install it that way? Rip this thing out."
A large number of people run their TV2 diplexed to their existing prewired cable, so that no wires are exposed. Can't do that with HDMI. Any idea how difficult it can be to run a thick HDMI cable so that it is hidden? It could take hours to run a single cable.
And what if the TV2 is 150' away, or there's no direct path? What it if is only 75' away? Who is going to be buying those $200+ HDMI cables for the customer? It isn't going to be Dish. They just aren't going to be spending all that money for TV2 installation just so their customers can pay them less per month.
No, once you look at the reality, it makes more sense to put a receiver at each HDTV.