Tax payer subsidies in the form of 'bail outs'.
That and by making some of the cheapest cars out there with substantial incentives attached. A Chevy Malibu (Impala, whatever the model is today) - may MSRP the same as a Camry. But the incentives and the willingness of GM to finance folks at 16% APR means they continue to sell cars.
Then there are fleet sales of trucks, which remain a huge portion of GM's business.