Non-US guy here. I don’t get why there’s a choice whether to vote for him or not, when you know the alternative is Trump.

It’s clear Biden isn’t a great option, and there’s probably plenty of reasons not to want him. But is any of those reasons gonna get better in the next 4 years when his opponent would win?

Not everyone wants to vote strategically. Giving a candidate your vote is a form of endorsement. If I was a US citizen, I’d vote for Biden, and try to convince all my friends to do so, too. But I also understand the people who can’t bring themselves to vote for a guy supporting a genocide, no matter what the alternative is.
They’re basically saying “fuck it, if the system won’t give me a choice to vote against genocide, then I’m not participating in that system.”

The problem is, not voting is as far as they’ll actually go towards “not participating in that system”. They still want all the benefits that they get from the system.

So it becomes less of a politically motivated action and more of just a tantrum.