The Billion dollar "membership" fees probably went directly into Trump's pocket

Probably not. They were just never paid. It wasn't laundering bribes. It was just a fake. All those countries made "commitments" to pay the money, but they never paid any.

Trump's motives were venal - he wanted there to be a huge pot of money to be spent on stuff, and which he would have control of. That would have given him lots of chances to wet his own beak, self-deal, steer business opportunities to allies and relatives and anyone willing to kick some back to him.

But it never happened. All the countries who he planned on giving up the money quickly realized that there was not going to be any rebuilding in Gaza, and so no reason to fulfill their "commitments." And since Trump also realized that there was never going to be any rebuilding in Gaza, and thus no opportunities to wet his beak - so he didn't press the issue.