Just speaking from the US side of things, there aren't any 20/30/40/80/120mm AA rounds being produced in mass quantity and it is more of a scaling issue. System

Just speaking from the US side of things, there aren't any 20/30/40/80/120mm AA rounds being produced in mass quantity and it is more of a scaling issue. Systems like CIWS are also incredibly bulky, requiring a few semi trucks worth of equipment to operate. There are some German AA guns that have been used for counter UAS, but their export laws are a fucking nightmare to deal with if you ever want to sell, give or trade those systems later on.