Really the seed is only a number. Why they decide to only give that number to the host teams I don’t know. But for example, Michigan was for all intents and purposes the 17th seed, they just didn’t have the number next to their name. Oklahoma had the 32nd, 33rd and 64th seed in their regional etc.
They probably just don’t want teams to get caught up in the minutiae of we should have been the 29th seed but got the 36th seed instead! Also there’s a geographical factor although you wouldn’t have known it from the Orlando Regional. Typically they put together teams in close proximity or try to.