Shelf life doesn't matter if you are firing them as quickly as you can make them, especially if you actually can make them as quickly as you need them because they're so simple.

Right. High-volume users can skip the thermal batteries with decades-long shelf life, and just spot-weld a few AAA batteries inside the weapon. Just stencil the thing "Best if used by DATE". Good for a year or two at least. Skip the anti-corrosion stuff and ship it in consumer-grade shrink wrap. Ukraine ships drones to the field in lightweight cardboard boxes, not rugged weapons containers.

Many US weapons are really old designs. The Patriot went into production in 1980. The Stinger went into service in 1981. There's been progress since then. Consumer-grade parts can do most of what's needed.

AAA batteries don't have the current. Li-Ion is too fussy and has a pretty high self-discharge.

Ukraine can afford the cardboard boxes because they are fighting in their own country. The US has an ocean to cross.

Ukraine can get away with short shelf life because they are at war right now. The US has to stockpile because the supply chain has to run at some capacity in peace time to be able to ramp up quickly when needed, and discarding the produced ammunition after a year would be incredibly wasteful.

Neither Ukraine nor Russia can defeat each others' air defence networks. The US has a lot of experience doing just that, while successfully defending against ballistic missiles. High tier capabilities matter.

The Patriot in 1980 is a very different system from the Patriot that is fielded today. Between PAC-2 and PAC-3, AN/MPQ-65A and LTAMDS it's a cutting edge air defence system. The progress is constantly incorporated.

The Stinger is a bit old, but mostly because the US doctrine has few uses for it. Regardless, NGSRI is coming.