I read an interesting political science piece[1] about the fall of professional (i.e. corrupt) politicians and the rise of amateur (i.e. ideological) politicians.
The claim is largely that voters started to care more about politicians implementing their favorite policies than being the recipient of trickle-down graft. They started choosing zealots who (at least seem to) have uncompromising stances on issues which won't change later in their term for some reason. Needless to say, these sorts of politicians don't tend to be the moderate, nuanced type.
___
1. I wish I could find it, but it's lost in the mists of the internet.