Uuuurrrrgggghhhhh who do Democrats have such short memories???
I think it has more to do with an inability to see the world, or people in it, in multiple ways at the same time.
Bush was a poor chief executive many bad to disastrous policies and politics. But he simultaneously does seem to be a fundamentally decent human being, speaking out against what is broadly seen as obvious destructive evil.
It's hard to hold all that as true for some people. And it's even harder to translate it into an answer for a pollster.