But how did we get from the original plan of the map to the one we are today?
Israel tripled their land mass after curb stomping the outside Arab countries in 1967, then gave most of it back in the 1970s/1980s. The main thing they've never returned of that nature was the Golan Heights, and the offer to do so has been an on/off thing since I think the 1980s; except Syria is still... well, Syria.
This is what the Israeli borders essentially were from 1968-1978:
Which those "Palestinian Lands lost" pictures all go out of their way to ignore. And the only time the UN voiced a strenuous, "Stop that crap
RIGHT NOW" objection to Israel constantly claiming land taken in the various wars was when they began the moves to push into Egypt proper. When Israel backed off from that, the UN was perfectly content with Israel keeping all of that above even though it wasn't even close to what the original mandate had.
And now instead of using war, Israel just builds "settlements" to claim more bits and pieces of the land assigned to the Palestinians
It was assigned to the "Arab state" that never decided to actually establish itself (Egypt and Jordan just took all of the Palestinian lands), and was taken over completely by Israel when they were chasing the Arab countries out of the borders of the British Mandate for Palestine. The closest that ever actually happened to the land assigned to Arabs actually being
claimed by Arabs as a new state was when the PLO established governance for the Gaza Strip, and Israel recognized their government and withdrew their claim on the land and their troops.
In that respect, the UN complaints fall on deaf ears, since they've managed to be both hypocritical (they say the settlements are illegal, and don't like the lands gained during the various wars, but don't dare make similar statements to, say Britain about the Falklands even though Argentina says the islands belong to them) and ineffectual (say "Give the land back" doesn't work when there was no established entity before Israel took it to give it back
to, because the UN never bothered to actually enforce their original mandate so the Arab state could be founded).