If not for massive government bailouts GM and other "BigCo" companies would likely already be dead. In 2009 the US government dumped $50 billion into GM alone just to keep it afloat, taking a $10 billion loss when divesting.

The self driving battle is going to be complex, unprecedented, unpredictable, rapid, and probably dirty given the stakes. These are not generally the sort of conditions where old behemoths tend to shine.