> Because those 91% of the people could easily ignore the Democratic and Republican candidates if they were terrible (which seems to be the case this year), and

> Because those 91% of the people could easily ignore the Democratic and Republican candidates if they were terrible (which seems to be the case this year), and just vote for another party's candidate in the general election. Israel had proportional voting with a 1% electoral threshold (given there are 120 seats in the Knesset it's almost the natural threshold). They eventually raised the threshold more and more (3.25% now I think) because of the hyper-fragmentation which meant niche parties holding the coalition hostage. The degree to which a given electoral system represents voter preferences is highly election-specific. People are also usually not polled on their detailed preferences so it's hard to empirically determine which one is most likely to maximize the representation of voter preferences in a given country. Also the complexity of optimal voting strategies across electoral systems is different. An argument can be made that the simplest is the best. Say last year in Poland the mainstream consensus was that there's going to be a big coalition of all the parties against the biggest one. But some of the minority parties under-performed while the big one overperfomed giving the big one majority rule with just 37.58% of votes. If you'd redo the elections even the same week you'd probably end up with a much different result.