What has happeded to the show "Las Vegas?"

Does anyone know why:

Marsha Thomason left after first year? Big loss.

Nikki Cox and James Caan left after last season? Big losses.

I would be perfectly happy if Molly Sims all of a sudden became intelligent and stopped acting so bimboish.

I actually stopped making Las Vegas a "must see" this season. The script has really degraded.