From the perspective of realpolitik, I’m not convinced abandoning support for Israel will win him more votes from pro-Palestine groups than he loses from pro-Israel groups. Lots of moderate Americans support Israel implicitly.
Either way, it’s politically costly with no upside for him. I think Biden’s only hope on this file is for the Gaza war to end quickly before the next election, but I don’t see that happening. Looks like Israel’s plan is an indefinite multi-year occupation of Gaza under an authoritarian police state.
Can you imagine an ad with Biden's full throated support for Hamas/Palestine backed by pictures of the babies Hamas murdered in their cribs? Biden would get slaughtered for that.