> Fewer than 3/4 of eligible voters voted in 2020.
This is not completely true[0]. I'd also give the advice that you shouldn't take a "nationwide" average to mean much of anything. The wikipedia article shows wide variation across the states which is true for almost any statistic you can think of.
> actually vote in primaries
Bernie voters might give you a hint as to why. I guess this is the problem Mayor Pete's "shadow" app was meant to solve. It honestly seems like parties don't genuinely like people voting in primaries. The person who's "turn" it is might lose.
> elections that actually have the most impact
Unfortunately we're talking about the legislature here because they write the laws in question and are the proper party to wage your grievances against. Have you ever looked into how competitive those primaries actually are? Anyways this is why I vote for Greens and Libertarians. Then they might stand a chance of cracking 5% and getting recognized fully by the Federal Election Commission.
> Americans just don't show up to vote.
All evidence to the contrary. What they don't do is vote in senate elections. There districts with as low as 25% voter turn out. Which means you only need 12% of the eligible population to turn out for you to secure your seat. So you're right. No need to cheat. Just be arbitrary and capricious to the point that busy and worried people no longer feel that using their time in the voting booth can actually change something.
> It's a disquietingly under-informed and apathetic electorate.
As always, back to where this conversation starts, who should bear the responsibility for this? I don't think blaming the electorate itself brings you anywhere other than helping to chase people further away from an important civil institution.
[0]: https://en.wikipedia.org/wiki/Voter_turnout_in_United_States...