They can assemble things. But they probably just do not have the capability of mining all the things they would need to build ammo on a large scale. To my knowledge Israel does not produce any steel, they don’t mind copper they don’t have all the precursors to build the explosives and ammo. It’s a very small country. If they had an ammunition factory with that kind of capability, Today we would probably be talking about nations putting an embargo on copper, steel, machine tools, etc.
They actually have steel mini mills. They have iron ore, but don’t mine it.
There is copper ore in the Tinma area, but mining has been closed for environmental reasons.
For military purposes the critical requirements are oil production, steel production, grain supply. Then steel alloying elements and aluminum and copper.
I think Israel’s critical weakness is grain supply, They are self-sufficient in food, but depend on grain imports for animal feed.