Half of munitions missing means doubling the logistical burden of delivering the munitions to where they need to be employed. The trucks/plains/ships that carry your munitions need to be fuelled and protected, too, so the expense is super-linear, especially when it's a distant war and not a war fought on the country's own soil, like in Ukraine.

Cheap munitions sometimes explode before they are launched, killing crews and destroying platforms.

Cheap munitions mean that CAS is a roulette. You waited for ten minutes for a support fire mission? Sorry, wait for ten more, whatever we launched has failed. Or maybe you're dead because the munition has hit you instead.

Cheap munitions can pin you down. Those cheap FPV drones that are supposedly cheaper than Javelins require dedicated immobile units to launch and guide to targets. Javelins are organic to infantry squads.

Cheap munitions are either very expensive or impossible. There's no cheap anti-ballistic missile and no cheap missile that can sink a warship in the Taiwan strait when launched[*] from Guam.

[*]: alright alright an LRASM would need to be flown closer by an F-35 but the point still stands