What does the US have to gain? Location, pressure, denial of certain attacks (like Israel assassinating Iranian generals), being able to position nuclear weapons close to Iran, as well as distracting Iran from attacking US targets directly, among a host of other benefits. This also extends to other countries in the same vicinity.
Israel would definitely have the funds to take out Palestinians if they weren't being supported by external forces. The Palestinians are flat broke, they have no advanced industries at all. The GDP per capita for Gaza is like $900 USD a year per person, and only double that in the west bank. Israel is around $50,000. The British really turbo-charged the Israeli economy while they were in control of the area pre-1948 and the effects of that are still extremely obvious.