For the reasons mentioned so far. Initially the banks were still close to Obama I think. Jamie Dimon of JP Morgan Chase was considered a possibility for the treasury for some time but things turned a bit sour between them. I think Dodd-Frank wasn’t too popular either.
The one I find the most damning though is Jeffrey Immelt who was paraded by Obama initially and now Immelt is going for Romney which is a bit embarrassing for Obama.
Charlie Gasparino has written a book on the relationship between Obama and Wall Street and he goes into how Obama wowed Wall Street in 2007.