Buick is basically under the same pressure as the remaining near luxury brands (IMO, Acura, Volvo, Lincoln, and what VW has tried to be), plus the old person stigma.
Mainstream brands sell some pretty nicely equipped cars these days, as even Chevy's compact is no longer a penalty box.
The growth of leasing (more than half of all luxury sedans these days) and CPO programs has made outright luxury brands more accessible to more 'buyers.' With ze German cars, it also eliminates the worries of pricey out of warranty repairs for the first two buyers.