In the 1990's Nissan was suffering. On the brink of collapse. Even Nissan's Japanese CEO admitted failure on his part. Stating that they just didn't build the kind of cars that people can be passionate about. When Ghosen took over, he formed an alliance (not a merger) with Renualt, consulted Nissan's younger engineers and brought new ideas to the table. They put forth a new effort on a clean slate and in record time righted Nissan's sinking ship.
What you are seeing is history repeating itself. GM is doing what Nissan did. In order to move forward it must wipe the slate clean.

In the 90's Nissan's line up was pretty bleak. Dominated by 4 door ho-hum cars. They had a couple of bright spots with the 300Z and the ill-selling 240sx. But mostly, they mass produced sentras and altimas, and base model maximas. Its not that the cars were bad, they just weren't enticing enough to get people into the showrooms.

GM and the big three failed to see their mistakes. Concentrating efforts of SUVs and trucks. They are guilty not of making bad vehicles, but not making the right vehicles. They just have failed to listen to the broad customer base.

The other reason they are hurting is a complete lack of consumer faith. For too many years the completely unfair notion that domestics exhibit lesser quality has finally caught up. I hear it all the time, "American cars are crappy." from some dumbass that knows shit about cars. This gets spread around enough until it penetrates the consumes psyche.