GM has for years now been downright abusive to their suppliers, including key suppliers with whom they have long relationships.
I have been in the past a supplier to GM, and I have friends who are today, and the consensus is that dealing with GM is just not worth the aggravation any more.
They haven't realized that it's not their suppliers' fault they can't make money - it's the miserable products they offer!
There are a few bright spots in the morass. For example, any large or mid-size GM product that uses the 3800-series V6 is a keeper. These cars hold their value well, and top the charts at Consumer Report year after year.
My 2001 LeSabre is a great example. It seats six, has 200 horsepower, gets 30 mpg on the highway if I keep my foot out of it, and it cost me 6500 bucks. I let somebody else pay the depreciation. =]