> hasn't Israel already offered them multiple treaties that would give them ownerships of large sections (as in nearly 90%) of the disputed land, which Hamas has just rejected out of hand?

No. You should provide sources for such a claim.

Here's the last peace deal offered and the only one to include formal borders. It was rejected by the Palestinians (who weren't invited to the meeting) and the Jewish settlers organization

https://en.m.wikipedia.org/wiki/Trump_peace_plan

Edit: Hamas has rejected peace offers, the Palestinian Authority has not rejected any offer for "90% of disputed territory" nor has such an offer been made