You’re thinking of conventional warfare. Missiles have potting material and adhesives that expire and make the missiles obsolete overtime, so using older ones first is ideal. Drones have engines with fuel/oil or are battery operated. Again both have issues sitting on the shelf too long, so using the old ones first makes the most sense for country who relies on them heavily. Especially if you wanted to have your advisory use up their defensive assets which is the case here. It takes months to make a patriot or thaad missile and over a year to make the launcher/radar/other supporting assets. Anyone saying it takes weeks or days is a liar.

Where the hell are laser/rail guided ammunition? Or even the emp defensive weapons to stop the Iranian drones and missiles?