Well, it would be quite easy for the USA to stop, then, if Israel is in such a nice position. Why doesn't it? Israel should in fact be asking for that; no more Congress getting its knickers into a knot when Israel uses some super cosmo weapon contrary to US Federal law.
The problem is that the Israeli left loves the money, as they funnel it to prop up the Israeli welfare state, which is stiffling Israel. Moreover, the Israeli left likes Israel's hands tied. In 1998, then Prime Minister Netanyahu (now finance minister) stood before congress and called for a stepped cessation of economic aid. Of course, he is a Likudnik.
"Well, it would be quite easy for the USA to stop, then, if Israel is in such a nice position. Why doesn't it?"
Let's review: Jimmuh Carter hosted the signing of the peace agreement between Egypt and Israel. In return for the principles letting Jimmuh take credit for something besides serving coffee, the US agreed to pay each country a bounty of some 3-4 billion dollars annually. That's why. It's a treaty obligation which persists AFAIK, in perpetuity.