[Zhang Fei]

I think your question could be rephrased:

Why do so many males seem to have a problem with marital fidelity

My guess is that males are simply wired that way (to go for attractive women). Whereas women are wired to go after high status males. Low status males don't get the same opportunities, because females tend to go for guys higher on the totem pole. Monogamy may simply go against human nature.

[William Tell]

Zhang Fei said: "My guess is that males are simply wired that way ..."

I don't think that "politicians" have a lock on status. To some women, driving a fancy car imparts status, at least relative to other men that can't even afford that.

Politicians who stray make the news because they have recognizable names and because there are political consequences to their actions. I doubt very much that politicians have affairs at a much higher rate than other men.