Why was Oldsmobile closed down? GM should resurrect it as a strictly r/d division.I thought they had good car

Sales where continuing to drop to the point to where the line was no longer making any money. And as the line was redundant with Buick and Pontiac, they opted to close it down. Why they don't open it as an R/D division, Well GM already has one, so it would make it redundant again.