Seth Stevenson of Slate wrote an article on Monday called "Don't Blame Voters for the Rise of Trump. Blame the Stupid Way We Vote." Slate isn't known for being particularly easy on the right-wing, so this is one of those "Only Nixon can open China" sorts of deals, and very much worth a read.
So let's assume you're wondering "why Trump?" I don't necessarily mean, "I hate Trump," as I think this is an interesting exercise for everyone (though Trump is of course highly disfavorable--even among many of his voters--but we'll leave that aside).
Stevenson makes all of the right arguments about why a plurality, first-past-the-post voting system creates incentives to not vote for your favorite candidate. He points out that the "establishment" candidates were pretty broken up early in the race and allowed Trump to get ahead with a small share of the vote. He even points out that he got the smallest overall margin of vote in a long time in the primary system.
His arguments work perfectly for the general election: if Trump or Clinton are your second-least-favorite candidates, then you'll be voting for them. Given Trump's disfavorability rating, it's likely many Republicans are voting for him as an anti-Hillary gambit, hoping he's not as bad as they imagine her to be. (It's likely much of this goes the other way.)
But the axe I want to grind is that we can't take responsibility away from voters for who they ended up picking. The GOP could have gone with someone else--or at least gone to a Contested Convention--very easily, if they didn't embrace Trump.
Trump ended up getting 45% of the vote, to Cruz's 25%, Kasich's 14%, and Rubio's 11%. He did scoop up a lot of that late in the game as people dropped out, but let's be clear: he wasn't totally railroaded into victory.
As folks like Bush and Christie dropped out from the Establishment Battle Royale, you had 3 not-Trump contenders left: Rubio, Kasich, and Cruz. Presumably Rubio and Kasich were splitting votes... but only 25% of Republicans voted for them. Rubio dropped out after losing his home state of Florida, leaving Kasich as an Establishment darling that could have consolidated the GOP if they were committed to stopping Trump.
As we pointed out in Episode 7 of ReConsider's Podcast, a brokered convention had a >50% shot when Rubio dropped out, assuming that Kasich/Cruz picked up his votes and Trump didn't get more popular.
But that didn't happen. Kasich picked up a few states but stopped after Ohio. Cruz got a few more small ones. Trump scooped up Republicans and started getting over 50% of the vote in later states.
Let's look at the incentives for later Republicans: if they didn't like Trump, they could have voted for either remaining candidate (Kasich and Cruz), and forced a brokered convention. They weren't in a weird game theory trap--and even if they were, that didn't involve an incentive to vote for Trump. If you don't want Trump, you don't vote for Trump--unless you want him way more than someone else.
It's possible that Cruz was so unliked by the GOP that they rallied around Trump to prevent his chances at getting the nomination (by preventing a brokered convention). That's certainly the incentive they're facing with Hillary Clinton. But Donald Trump was always more unfavorable--he wasn't the lesser of two evils, but just as evil. With two highly unlikable choices and one actually favorable choice, the incentive for an anti-Trump/anti-Cruz voter would have been to vote for Kasich.
So given the game theory, I think we can't say that Trump managed to get the nomination solely due to weird incentives from the way we elect people. He'd won over enough of the GOP, straight-up. When he hit the main stage, he had more support than Cruz or Kasich the whole time, and that's a reality we can't simply logic away.