More plausibly, US has now run through its stocks of weapons sending them to Ukraine, and doesn't have the weapons to send. Framing it as refusing to send the weapons because US all of a sudden developed a conscience is a way to avoid admitting this.
That this is at best a PR stunt and at worst an outright lie. This one shipment isn't going to do anything to curtail Israel's behavior and the shipment will eventually be delivered anyway.
Oh come on. This is pretty limp wristed narrative bait. There was one shipment out of many that maybe got held up, temporarily, potentially by accident, that's not the firm moral opposition to a genocide that we seem to think it is
Biden has been slow-walking arms to Israel for a while but there are forces that want to use Netanyahu's actions against him as if Biden has control of him.