That was actually a very good question, and one he had asked himself many times. Still, he hadn't come up with a suitable answer that covered all of Dumbledore's particular quirks, in many years. "I'm not really sure," he finally said, quietly, shaking his head. "I think, on some level, he did good things because he knew that was the right thing to do, but on another level, he simply enjoyed being in charge, and having troops to rally behind him. So the better the cause, the more people he could attract to follow him." He was basically drunk with power, and he likely would have become Minister of Magic, if that job hadn't come with so many tedious details to oversee. Better to have Fudge installed, whose strings he could still pull ... for several years, at least, until Fudge had become confident that he could manage quite well on his own, thanks.
He sniggered when Lizzy concluded that adult relationships were weird. "They are indeed," he answered with a warm smile and a nod.