It's been in the making for a long time. GM sold off their biggest profit maker years ago, which was the GM Finance portion of the business. The best performing brand they had underneath them was Corvette, but hey, it fills a niche market. Another fundamental problem, who was one of their biggest competitors???.....
...? Themselves. Just think about it for a moment. At present, their active brands include Cadillac, Buick, Pontiac and up until 2004, Oldsmobile. All brand names are synonymous with medium to large sedans, spanning the standurd to luxury range with a few variations within each brand.
Not only that but they were all building cars whilst paying no attention to changes in market trends. Why has Toyota gradually managed to eat up a large portion of GM's market share? Because people have been feeling the pinch of rising petrol costs and the cost of owning and running larger cars. Yeh, I know, americans don't care, they love their massive cars BUT.... The figures prove otherwise.
It's a dog eat dog, capitalist world. If you can't sell what the customers want to buy then it's over. And the writing has been on the wall for them for years.....