I don't have the answer, but thank you for asking. Seems a bunch of people want to sweep this under the rug, with the downvotes.
Explain Like I'm 5 (ELI5)
Easier to type out this way
Because the entire world watched and stood by mostly silently as the Jewish people were eradicated in Europe and only stepped up when they became personally threatened.
Then they decided to return the Jewish people to their homeland because 1) it wasn't theirs to give so it was easy and 2) it wasn't in their land so they didn't have to host them.
That is of course a vast oversimplification, but the spoils of past policies have come to roost.
Israel is surrounded by enemies and its currently elected leaders, paranoid beyond reason. Most see the Palestinians as largely innocent bystanders in a war between Israel and Hamas, not true targets, so they don't support the idea of genocide.
But many of us see Netanyahu as someone who will not stop with eradicating Hamas as that was never his goal, and to pretend that all of these accidental strikes are indeed accidental is infuriatingly insulting.
It's so difficult to thread the needle that both the Jewish people and Palestinians are embattled in a hostile region. There are good and innocent people there.
And those people are losing.
Edit because I stopped before truly answering: The world has been supporting Israel out of guilt after WWII and undoing that framework of support will take time, and of course Israel is trying to keep that support.
i'm not sure if that's a thing that can be easily explained. The middle east has a history of violence and strife for thousands of years. And yes, some people still call back to that. sure, the anti-palistinians who commented here have a point. some really do pretend that what Israel is doing is just and correct. Others even need to pretend that nothing is even happening. it's far away, so we can just try to ignore it.
whatever your cause and justification, it is genocide. NO MATTER what "Hamas" are doing (everyone in Palestine can just be called Hamas, you don't need any evidence. See the "war on terror" where everyone could have been called Taliban to justify ANY cruelty), the power imbalance is SO big, Israel is commiting war crimes. and no, that's not antisemitism. but people raiding food and aid trucks, civilians being spurred on to pillage villages, raizing entire neighborhoods, that's not a response. if that was the "correct" response, then every country would be a dead desert.
So, dear 5-year-olds, the world is a complicated place. and if anyone wants to give you a simple black-and-white answer, they're holding back vital context.