It is electoral suicide for the CDU in that position to govern with the Left Party or with the Greens. The vast majority of CDU voters are closer to the AfD than they are to the parties of the radical left.

The Greens are despised by the German right and center, because of the extreme climate cultism they shoved into the government (or are being scapegoated for). And the Left Party is despised for being former communists, and actually excluded the same way as the AfD has been.

It is electoral suicide for the CDU in that position to govern with the Left Party or with the Greens. The vast majority of CDU voters are closer to the AfD than they are to the parties of the radical left.