Because it seems like it might be a nice compromise to limit contests to specific bands. Say you schedule a contest and limit it to 20 meter phone. The contest happens on 2-0 and the other bands are clear. Next week you have a cw contest on 80 and 160. Then maybe the following week a contest on 10 meters using dipshittal modes. Then maybe an AM contest on 160 the week after. Then maybe a phone contest on 75 and 40 the next week,. Then maybe a qrp contest on 15 and 20 the next week. It seems to me that by going this route we could have more contests, more frequently and without compromising anyone. Plenty of band space for contesters, plenty of band space for non-contesters, greater diversity, greater flexibility, and less issues. I think it would be a win/win for all.
Other hobbies and interests I have seem to allow for people to compromise and create balance. It doesn't have to be all or nothing. Unfortunately ham radio is the one hobby that seems to take the "all or nothing" approach. Why is it so difficult for hams to compromise ? There is more than enough room for contesters and non-contesters alike.