Why did Dish have that push to add all of those smaller markets, i.e. in the 150-200 range based on market size ?
That was because there is a clause in the new SHEVRA law or whatever its called that if Dish could carry all the DMA's they would be out from under the penalties imposed when they got caught providing distant locals to those of us who were not legally entitled to them. Because of those penalties dish could not even provide service outside a DMA to an unserved segment, i.e. if a DMA did not have a FOX station they could not import the neighboring DMAs FOX station. I believe it also freed up their ability to carry significantly viewed stations from neighboring DMAS. It gave DirecTV a competitive edge in locals.
To answer the question why do Satellite companies want to carry locals - because locals are the most heavily watched channels, believe it or not, if Dish or DirecTV dropped locals, they would lose a lot of subs.
Another part of the law requires that if a carrier carries one local station in a DMA in HD, then they must carry all the full power locals that are broadcast in HD in HD also. However if a low power station or a subchannel is in HD the carriage is not required, but the station that owns it may negotiate that in their retrains agreement.
So if your ABC or FOX is on a sub channel of a full power station, the carriage of it in HD is not mandatory, but negotiable with the station.