this blackout is a regional blackout to prevent people from seeing the game on the NFL network instead of local station it's only for preseason. it's a pain but the local station owns the local rights to the game and they are the one s placing the blackout, not Dish, not NFL Netowrk, the locals stations. the reason why is they want local ratings for the game in their area.
example: if you live in Dallas, tonight's Cowboys/Ravens game will be blacked out on NFL network due to KTVT 11 owning the local rights to the game, so DFW area Cowboys fans need to watch 11 in order to see the game. as in KTVT is enforcing the blackout.