Why do people recognise the Egyptian claim to Gaza and Jordanian claim to the West Bank, without mention that these lands belonged to Palestine in 1948? Why does Israel get flak from other countries for occupying lands that belonged to Palestine initially but taken by Arab states following the 1948 Arab-Israeli War? Wasn't Palestine supposed to have Gaza and the West Bank? Can't they then form Palestine from these lands that was given to them in the UN Partition Plan, if the Arabs were their allies?
For a start, Egypt never formally claimed Gaza as part of its territory, and it did indeed try to set up Palestinian figurehead administration there, firstly the All-Palestine Government in 1948, which lasted until it was abolished by Nasser in 1959. Supposedly, he intended to later put the PLO in charge of Gaza, but never got around to it before the Six Day War.
Jordan did formally lay claim to and annex the West Bank, though this went largely unrecognised internationally (though this is a much more vague and less significant occurrence than is sometimes portrayed). West Bank Palestinians were made citizens of Jordan (whereas they were not and have not been made citizens of Israel under their occupation). So there were two reasons for the lack of a Palestinian state in the West Bank - i) Jordan wanted to keep the land, and ii) Palestinians had civil and political rights there, so little incentive to separate.
Also, the Arabs were only really "allies" in a nominal sense. They had different, often conflicting, aims, and didn't co-operate much.