I’m not sure where you think the money goes, but buying munitions from American companies and shipping them elsewhere doesn’t take money out of the country. Moreover, this is probably a handy way to get rid of old military stockpiles. “Here, have these last-gen rockets. They cost $x. Meanwhile, we will buy current-gen rockets for $x for ourselves. And now we can (rightly) say we donated $x to the war.”
Whoops, didn’t see this was for Israel. While I don’t agree with their stance, the financial principles still apply.