"25% sympathize more with Israelis than Palestinians while 15% feel the opposite."
True enough, but crucially Republicans are overrepresented in those 25%, and being Republicans they can be disregarded for the sake of Democrat electoral strategy.
For example, more Republicans than Democrats (46% vs. 10%), ... sympathize more with the Israelis than the Palestinians
See also: https://apnorc.org/wp-content/uploads/2024/10/Pearson-AP-NORC-2024-Report-Final.pdf page 11.
The numbers are this bad in part because Republicans are morally bankrupt, which isn't really news. Another poll with more focus on partisan politics from the same time period got this result:

That reflects a success of propaganda. Notice that the other strong option for why they might not have voted for Harris was "the economy," even though Trump is an objective catastrophe for the economy and Biden pulled off a minor miracle for working people even having come in during still-pretty-apocalyptic conditions with double normal unemployment and a big chunk of people still dependent on Covid assistance.
Trump economy voters are nuts no questions asked, but it should be stressed that the only reason that propaganda was so effective is because the Biden/Harris campaign, and later Harris/Walz campaign, gave it room to be effective. Biden said he was going to keep doing what he was doing, which simply wasn't enough. He also claimed that the economy was good when it really wasn't and patted himself on the back for it, which was just... no. More people than ever were (and are) living paycheck to paycheck and the dunces in the DNC decided that campaigning on status quo politics was a good idea. GOP propaganda also had a big role, don't get me wrong, but this was an it takes two to tango affair.
The relevant question isn't "did some people decide that Harris was responsible for the war in Gaza and decide not to vote as a result." Of course the answer to that is yes. The question is "did more people decide that, than the people who would have decided that she was supporting terrorism if she took a different position, and made her lose even harder?"
From the data above, I think the answer is a pretty clear no. For example, 67% of Democrats put reaching a permanent ceasefire between Israel and Hamas as very important, while 25% put supporting Israel in the war as very important. And, perhaps more importantly, pro-Palestinian voters were much better positioned to tank Harris's campaign in crucial swing states compared to pro-Israeli voters, who are more evenly distributed.