The reason countries pour aid into elsewhere is for trade/development opportunities they wouldn't otherwise get. It was colonialism before - now it's zones of influence - but the motivation is the same. It's usually backed by mitary strength, but isn't usually one-way since the country also benefits from the infrastructure development and resource extraction which they wouldn't otherwise have the money (or expertise in many cases) to do themselves. Trade is mutually beneficial.
The US already pours enormous amounts of money into the region. It isn't only Israel who gets aid ($3 Billion a year). The US also give $1.5 Billion a year to Egypt, $1.7 Billion to Jordan, and $0.5 Billion a year to the Palestinians (who also get another $0.6 Billion from the EU and $0.2 Billion from the Arab states). That's normal aid, without any rebuilding.
The US obviously do expect to benefit from those huge sums of money: mainly that the increased stability in the region means that they can do (mutually beneficial) business there. And there's the occasional political favour.
I can't see the US funding the rebuilding of Gaza unless they get some benefit. I suspect that Trump's recent announcement is as much as anything a signal to the Arab countries. The US are willing to do xyz. If that's not what other regional powers want, then they need to step up now and propose an alternative.
I don't know whether the Arab states will. I'm not sure that anyone wants to pour billions into rebuilding Gaza when it's likely that the conflict will restart in a few years. Not sure where that leaves the Gazans.