The reason the Palestinians did this is two-fold; Fatah failed them and they want the destruction of the Jews. Fatah is/was a corrupt organization that did not provide for their people, at least if you believe the interviews with Palestinians on the street. The Arab world's hatred for the Jews goes back many centuries before the creation of Israel. The amazing thing is if you do your research you will find that there are no indeginous "Palestinians" to that region. The Arab/Muslim people who populated the barren land which became present-day Israel were nomadic people of Turkish, Cypriot, and Arab descent among many others. The Jews who built the current state offered and payed much more to those people than the Arab landowners who oppressed them.
Edit: Hamas' campaign included feeding the poor, setting up schools, and generally providing more support for the Palestinians than Fatah had in their reign.