a genuine answer from an arab who spends a lot of time around arabs:
the thought is if we don't vote for biden now, it shows that there is an important bloc of people for whom support of palestine is non negotiable.
while this means a win for trump in 2024, in 2028 it means the democrats will have to run an anti genocide candidate if they want to win
commented this elsewhere, but the general idea is that by showing that an important contingent of the left won't vote for a pro genocide president, the democrats will have no choice but to run a candidate that is electable in the future.
this means that trump might be president in 2024. That sucks, but most of the damage has already been done (supreme court, senate, etc). Might as well show the dems that they have to run a candidate that supports the rights of civilians all around the globe