It's not just about watching football during our bad seasons. It's about the integrity of the game. If poor teams lose on purpose, that effects the top teams. If the Dolphins lost to the Pats in week 17, the Pats get the bye, the Chiefs don't. Maybe the Chiefs get knocked out in round 1, or maybe they suffer an injury they otherwise wouldn't have and lose later. Maybe the Pats are the Superbowl champs this year with that bye. Teams like the '07 Giants maybe don't make the playoffs if a bad team loses to the team competing with those Giants for the last playoff spot.
It's also about being able to enjoy each and every game when your team is good. Wins against non-playoff contending teams would have no meaning if they are losing on purpose. If the Dolphins were a top team (in a league where the bottom teams lose on purpose) why would I care to watch any Dolphin game against a non-playoff contending team? I know it's going to be a win, there's no point to even watching.