If you track
bracket matrix, each team's seed (assuming they're not a bubble team) is based on the average of 100 published brackets (there may be some weighting system, not sure), so the seed usually lands on a decimal number. Illinois' is currently 6.17 as of this morning.
So, to
@21ChampaignSt 's point, if you're between two whole numbers, you're more likely to be seeded with the whole number before the decimal (Saint Mary's is 5.9 and considered a 5 seed, whereas Gonzaga is 7.83 but an 8 seed, so this varies).