You’re looking at things through there lens of 1 election cycle.
If a third party that’s against the genocide Israel is carrying out gets say 5% of voters in deep blue or deep red states would that not be a signal to the democrats that they should change their stance before the next election?
Not funding and supplying a genocide seems to be a pretty clear and easy issue to change especially when 60%+ of democrats are in favor of it. We’re already violating our own laws by continuing to do so.
The democrats are already moving to the right even with the left continuing to vote for them. They think they can win over some centrists republicans (even though they can’t in a meaningful number) by adopting right wing policies while not losing the left because at the moment they know votes are guaranteed because “republicans worse”.
Having voters in areas that effectively don’t matter this cycle show there displeasure in the genocide we’re enabling is the least we can do to counter it.