^ of course no one will stop selling weapons

, but if you can inject a bit of pressure in the negotiations you are maybe in a better position to put through some additional interests, may it be price, strategy or politics. And while it does not make anyone more trustworthy, it is a sign to S.A. that the US will still maintain ties and share intelligence.
If you just hush it up, your standing will not be better than if you did what you did now, in the eyes of the world. And it gives a broad hint that such action as done by Mohammed Bin Salman does not get unnoticed, even between allies. Yes, no one should have diplomatic ties with such regimes let alone sell them weapons, but .. China, Russia .. and it is better to keep up speaking with another. Better than what was done in the last years.
https://de.rt.com/nordamerika/106594...audi-arabiens/
Yes, RT, i know ..