Another reason to soft lock a sector for awhile is if all of your other sectors in an area are going to get taken earlier, having a sector that is viable later gives you a foothold to rebuild in that area without having to retake all the way across the map. This can be especially important in the center two rings, and with very active guilds on the map.
The only time I see guilds "trading" sectors is when there are only two decent guilds on a map. It's not their fault that the other guilds can't keep up with them. If you get 3 or more extremely active guilds on a map, swapping sectors never works because the third+ guild(s) are too strong to let that happen. If you only get one strong guild on a map, then they lock the map and are screwed for battles for the rest of the season. Just the way it goes. If your guild gets locked out of play by guilds "swapping" sectors, it is purely on your guild for not being strong enough to compete. Brutal but true. Kinda like the real world.