Israel is currently dependent on external munitions suppliers, which do not necessarily need to include the US. Israel did leverage US assistance to shoot down Iran's drone attack, but it also leveraged Arab state cooperation. It is probably not the case that Israel is existentially dependent on US military aid. It's worth remembering, though, that Israel wants that aid, and also wants the tacit endorsement of the United States, and is acutely aware that one of our two political parties is more committed to Israel's current leadership than the other; read anything they say with a grain of salt.
If the US and EU countries were to cut Israel off, what other options does it have? Russia is already importing various weapons, a good part of them from Iran, who will absolutely cut them off if they start helping Israel. India and Pakistan are not sympathetic to Israel. Arab countries will feel internal pressures if they become major suppliers to Israel. Who is then left? Would China really wade into this conflict, and endanger their own relations with the Arab world?
Their second largest trading partner is the second largest munitions supplier in the world. Further: the Arab world is not in fact aligned against Israel. They are much more concerned about Iran than they are about Palestine.
None of this is going to happen, because everybody involved is aware that Israel would be sustainable after a realignment away from the west. Everything gets worse for everybody (except China) after that occurs, so it won't be allowed to occur.
(It's further mooted by the fact that opposition to Israel is largely an Internet phenomenon; Israel enjoys broad, bipartisan popular support in the US, Gaza is at the very bottom of polled issues in order of importance to the electorate, and a very significant chunk (possibly more than half) of people rating Gaza as important support Israel.)
I did not say that the Arab world is united against Israel. However, there is significant anti-Israeli public sentiment everywhere in the Arab world, even more so than against Iran. Even if Arab leaders are not as sensitive to public sentiment as more democratic countries, they can't easily ignore it entirely, and becoming the main supporter of Israel is not a comfortable domestic position for any Arab leader.
Also, you are grossly misrepresenting public opinion in the USA and the EU. In the USA there is a significant and extremely vocal minority, especially among the Democratic party base, that deeply care for the genocide in Gaza. This has been visible in the major student protests, and in the significant protest votes in Democratic primaries (>10% undecided in some states!). And given the extremely tight election, this is very likely to cause issues for Biden. Now, whether reversing support for the genocide would cause larger issues is debatable, but I think unlikely - as most of the avid Israel-can-do-no-wrong supporters are not going to vote against Trump anyway.
In Europe the situation is even more difficult for the pro-genocide camp, as the population, especially in Western Europe, and doubly especially among the significant Arab, Pakistani, Indian, Turkish, and North African immigrants, is much more sensitive to the issue of colonial genocide.
The student protests, which are for obvious reasons not representative of the whole population, are themselves numerically a small portion of the faculty and staff at the institutions they're taking place at. Excellent recent examples of this: repeated instances of walkouts or sit/stand protests at commencement ceremonies, where everyone involved is arranged out on a field, almost as if to make these kinds of tallies easy to make (but serious tallies of protests at Columbia, Chicago, and UCLA have also been made). It just doesn't take a lot of people to make a lot of noise.
The "10% undecided" thing is a statistical null result, mirroring the last Democratic reelection campaign (Obama's, against Romney), which didn't include any attempted organized effort to lodge protest votes with "undecided" and still ran up those counts.
Polling --- Pew is a good place to start --- shows Israel below every other "major" issue, even among 18-29 year olds --- except (ironically) student debt. The issue gets less important as you go up in age brackets into cohorts that actually turn out and vote.
The groundswell of support for Palestine in America is, I believe, largely an Internet phenomenon. It's easy to forget that we're the weird people who tune in to this stuff. Most people just live their lives, and, for reasons that are straightforward to understand, care a lot more that a 12 pack of Diet Coke got weirdly expensive than about whatever is happening across the world. We have the same problem marshaling support for Ukraine!
