Because it's easy when you're dividing somebody else's country! Yes, a two state solution is probably the only one that will result in lasting peace, but there is a strong faction in Israel to cling onto all of historic Israel (ie. a country that, prior to the 1940s, hadn't existed for a couple of Millenia) - and many resist the limited pull oout from Gaza (not part of the ancient Kingdom of Israel). As for the US, support for Israel is popular with the powerful Jewish lobby and to a lesser extent with the (far larger) Fundamentalist Christian lobby, while the Arabic vote is relatively small, so US policy is liable to be pro-Israeli, particualrly in an election year.