Because, you know, DISH’s stuff fits on a regular mast. And their dishes aren’t any smaller than DIRECTV Slimline dishes. It’s just a little bit of frustration that a 1.5″ or 1.66″ outer diameter mast won’t work for DIRECTV Slimline dishes. There’s an adapter that can be used but in a best case scenario it does put a heavy load on a traditional 1.66″ mast.
DIRECTV chose the 2″ outer diameter mast at a time when it looked like the industry was going in that direction. The SuperDISH satellite dish (no longer used) also used that larger mast, and the WildBlue internet dish uses it as well. using a larger diameter mast allows for the mast to be more stable and also a larger diameter mast can be made more cheaply than a reinforced smaller diameter mast.
At this point, DIRECTV is firmly committed to the larger mast; almost all of their installations are done by DIRECTV technicians carrying their own equipment. No professional installer is going to use an existing mast, so DIRECTV just doesn’t see a need to change this sort of thing.
The other thing that needs to be considered is that DIRECTV is alone in using Ka-band frequencies for some of its satellites. Traditional wisdom is that the Ka-band satellites require a better aim in order to be more resistant to rain fade and that the larger-diameter mast helps keep the dish steadier. It’s true that Ka-band frequencies are more sensitive to rain fade, but the rest of it may be a bit of a stretch. You can say that the thicker mast, if made of the same material as the thinner one, presents a larger base for the dish and that maybe that translates out to better stability but… I’m not sure I buy it.
At this point, the bigger mast isn’t going to go away, because from DIRECTV’s point of view it isn’t hurting anyone. The folks over in corporate tend to look at this as a non-issue, even though it does make it a little harder for those DIY types like the people who read this blog and the people who shop at SolidSignal.com.