More friction though! and moisture is sucked into the hub as the air in the body contracts, think nice warm day, heavy downpour cooling contraction,
I'm not sure whether having no seals on the inside makes this better or worse - One seal may allow any drops of water to disperse into the larger centre volume rather than being trapped between the two seals.
Schmidt hubs - with a lot of volume have a tiny breather hole in the centre of the (hollow) axle to avoid this problem.