The UN or ICC or whoever are not the world police.
They are supposed to be, though, and would be if the Big 5 on the security council would let them.
what they can do at this stage is very limited.
Especially since they're hamstrung by the dogged US government insistence that everyone's eyes and ears have been lying about Israel for the past 75 years.
Given the history of the land and amount of casualties, I'd be generous to Israel to even attribute 50% of the fault to Hamas, but I'd like to hear why you believe they are at fault for 90% of it? Got no stakes here outside of the humanitarian crisis, just want to understand better.