Dish has been known, as commented above, to do some pretty serious compression on some channels, like SD, HSN, News channels, and any channels that don't get watched very often. The Hopper reports back what you watch and for how long. That's the way Neilson and the other ratings companies get it's ratings with today's tech without the old boxes they installed on peoples TV's.
Dish also sells (anonymously) the same statistics to networks and content providers. Everything they do is for $$, So shows that don't much viewership get reported back to the networks and therefore that's why a lot are cancelled. The networks then take the accumulated data from Dish, DirectTV, Spectrum, Cable TV, etc and decide the fate of a show.
As for the channel feeds, the same thing. Dish has algorithms that really don't care what you watched but accumulates the total time in people watch time of a channel which is tuned.
If in a month or so, the time use of the channel is low, then Dish will start compressing that channel.
If in a period of time a channel has a lot of time accumulated (like Hallmark, if you notice that's one of the better ones) then the compression is less. Same as in the movie channels, SD channels are compressed a certain amount but the HD channels have much less compression.
There is only a certain amount of bandwidth available per transponder on each Satellite. So they will squeeze as much as they can on a transponder leaving another one with less load that they can send up higher resolution (but still some compression) signals.
So, it's both marketing per show (like reporting back to the ratings companies) and also usage per channel. Less viewed channels will be compressed more as less people watch it.
And that was only my 2 minute elevator speech on Satellite broadcasting!