I think people were more happy Brock lost it than happy Seth won it. Plus folks tend to be negative on Sheamus since he's injured folks in the past (no one recently, but idk if there's a statute of limitation on being mad at someone about that).
But somehow, he got over with the Burn It Down stuff, so I can't fault them for going with the guy.
If history is any indication, once the afterglow of having a Universal champ that's actually around every week wears off I think crowds will tire of Seth.