I can think of a couple of reasons that are more plausible.
First, if I remember correctly, Dish didn't exactly manufacture a very large quantity of 1000.4 dishes and LNB's. (At least, not when compared to the number of 1000.2 dishes and LNB's in existence.) So, it is possible that Dish is running out of stock on that model. Therefore, they may have felt that it is not a good idea to continue to put locals on a satellite (77) that specifically requires that model (1000.4 EA) for a standard installation.
The other factor to consider is "moving" (or using a service address other than where you are actually located). On the one hand, putting some CONUS local markets on 72 makes "moving" to those markets easier, by making them available with the more standard 1000.2 dish. However, the real factor may have been that using the 77 satellite made it much easier to receive those signals in Mexico, where people are not supposed to be subscribing to US Dish service at all. (Dish has a separate Dish Mexico service for them.) So, another likely reason for this move was to crack down on people illegally receiving US network service in Mexico, and try to get them to switch to Dish Mexico instead.
Just my two cents.