James Surowiecki in the New Yorker considers an alternative explanation (h/t Ben Smith).

“The money the government has been giving the automakers has been going not to shore up their capital base, but literally to pay their bills. In the absence of government aid, the automakers would have had to shut down their factories because of their inability to pay suppliers and workers. That’s not true of even the most troubled big banks, which are having no problem meeting their debt payments or paying their bills: the government’s aid has gone instead to replenish their capital and allow them to stay in regulatory compliance. That doesn’t mean the government’s aid was not essential, but it was different: the money the government gave G.M. has already gone out the door, while in the case of the banks it’s still, for the most part, sitting on their balance sheets (which is where it’s supposed to be).”