I'm not USian, but here are some assorted reasons why one might choose not to vote. I do not necessarily agree (or disagree) with any of them, and this is my attempt at a reasonably balanced analysis as a person who is not an expert in politics, but has read a lot of arguments in the comments.

1. Voting makes you complicit.
   (Let's say for the sake of argument that it is a given that Democrats will continue aiding Israel's genocide and ethnic cleansing just as much as the Republicans, but will improve things for marginalised communities domestically.)
   The argument here is that voting for a politician that will perpetuate a genocide makes you complicit in a genocide in a way that inaction does not. The counter-argument is that refusing to exercise what influence you have in the choice between make a choice between Palestinian genocide or Palestinian genocide and trans genocide makes you complicit in trans genocide. This is literally the kind of thing that the trolley problem thought experiment was made to explore.

2. Voting for the lesser evil increases harm in the long run.
   The argument here is that demonstrating a willingness to vote for the lesser evil - with no red lines whatsoever - incentivises Democrats to only ever be slightly less bad than the Republicans, whereas having red lines and allowing Democrats who cross them to lose will incentivise the Democratic party to change their policies. The counter-argument is that Dems haven't exactly demonstrated that they willing to adopt certain policies even when it would be demonstrably beneficial to their election prospects, and so the pragmatic thing to do is to delay harm for as long as possible to give a better chance that non-electoral politics will shift in the interim. The counter-counter-argument is that such a shift will not occur while that harm is being delayed, which leads us on to...

3. Accelerationism.
   (Yes, I'm aware that what I'm about to write isn't the original meaning of accelerationism. Don't @ me.)
   The argument here is electoral politics either can never progress toward socialism/anarchism/your-flavour-of-leftism (if you're a leftist), or even that it is no longer even capable of halting a descent into fascism (if you're a pessimistic liberal), and so we should simply allow shit to get fucked so that a critical mass of people have it bad enough to do some revolution and/or non-voting-based direct action about it. The counter-arguments here include, but are not limited to: a) well, that's just like, you're opinion, man; b) that's an awfully big gamble to take when there's no guarantee that what will come after will be better; and c) you should prioritise the lives of people that currently exist, now, rather than those of hypothetical future people, and immediate harm reduction is of more benefit to those people specifically.

In case any one cares, I'm English. My position on voting is that I may vote in an election where the Greens or possibly the Lib Dems stand a chance of winning, but otherwise I spoil my ballot. Yes, I'm aware that the Lib Dems are shitlibs. Still better than Labour. I will never vote Labour for as long as it remains transphobic or as long as the likes of Luke Akehurst remain in the party.