I think your rhetorical question is exactly the right one to be asking. Or at least a variant of it. How do we end up with having to choose the lesser of two evils every election? It's been this way for the past several elections at least, but it seems to be getting progressively worse. And it's not just the major parties -- even our minor-party and leading independents have said some ridiculously screwball things that no one I know personally would have said.
There is something about the economics (in a broad sense) of our political process that brings the worst of our nation into the highest offices. I'll take a stab at answering this, but I'm certainly wrong and/or missing some pieces. It's really worth digging into though!
1) Human nature -> shocking, negative info is more memorable and motivating
2) Plurality voting -> 3rd-party spoiler -> Exactly two parties -> Mud-slinging becomes optimal politicking strategy
(1) and (2) lead to nearly 100% mudslinging, so it's perfectly natural for us to focus on how evil our candidates are.
On top of this, we have huge amounts of money now being spent by both the DNC and RNC, which are using increasingly-large datasets and the tools of the scientist to hone and optimize their election chances. Therefore we are inundated with 21st-century propaganda and demagoguery on a daily/hourly basis. Even those citizens that are well-educated can't help but be influenced.
The kinds of people who are best suited for government would never want to get involved with all this, and hence would never even register on the radar of the public and would have no chance getting far in a political career.