For the US Army the Phalanx is an affordable (read cheap) off the shelf solution.

It utilises spare explosive ammunition left over from the retired Vulcan system and an automated quick reaction capability combined with a high cyclical rate making it a desirable solution.

That and they can just get USN personel to maintain them.
One of my LPO’s just did a tour working on an Army Phalanx and he said it worked very well.
Also the Phalanx has another advantage, it was designed as a pretty much bolt on stand alone system that doesn’t take up any room inside a ship, so all the Army had to do was bolt all the equipment on the back of a semi-trailer.

I’ve been lurking here for a few months now but this is my first post…

The Mk41 crane isn’t used underway anymore, in fact on the Burkes the foward one is pretty much not used any more and the aft one is just used to help move torps from the magazine up to next to the tubes.