The problem was that US automakes have been shortsighted for years. GM made its decsion in the mid 90s when it dedicated so much of its plant capacty to trucks and SUVs, while ignoreing any imporvment to its mid and full sized car lines(this is the segment that the big 3 were known for and what made them unique).
Now the platforms that GMs mid and full sized cars are based on are close to 18 years old, their designs look unispired, and while their drive trains have become better(The Impala SS has a V8 finally), it is far too late, at least 10 years too late.
the new Buicks sedans are quite nice. the Lucerne has far more styling appeal than an Avalon for example. Reliability is still an issue, but GMs cars are getting better.