The simple answer is that the ball valve likely has fewer parts.

Nothing is ever that simple, of course. The two are so different topologically that they are probably manufactured on completely different machinery in completely different factories, and subject to oversight by completely different AHJs.

OR, it could be that you ordered a PSV from an outfit that makes them in batches of size other than one unit, on demand, and they had to wait for some more orders to come in before changing their flexible factory to make the parts you need.

Mike Halloran
Pembroke Pines, FL, USA

Thank you