I don't recall the Israelis bought the land in any way. Also previous to that the Palestinians inhabited it and had their own government.
This only happened in 1947 so many of the original people involved in the creation of Israel are still around today.
Throughout history people that this happened to tend not to be happy about it. The Palestinians want their country back and may well keep this up until they get it.
Most of these arguments boil down to the Law of the Strongarm. If say the Russians came to the US and told all the people to clear off except for the Indians and then protected them it would be a similar situation. The people kicked out wouldn't be happy about it and many would become soldiers and terrorists to try and get the US back.
No doubt the bitterness would continue even after several generations.