Pontiac, Saturn and Hummer wer discontinued as part of the 2009 bankruptcy filing. What GM learned, painfully, in the Oldsmobile situation is that franchise value has to be compensated to dealers when you choose to shutter a marque. I think it ended up costing GM $2B to compensate all the former Oldsmobile dealerships. When the bankruptcy arrived in 2009 it was the ideal setting to scuttle the lines that were not performing - the franchise agreements were terminated within the bankruptcy and dealers were compensated very little by comparison to the Olds denouement.
You left out Saab, GM destroyed them also.
They made good cars until GM turned them into crap.