Ukraine has shown that a drone factory can be made on any old building, it's not like they need huge machines. Would you carpet bomb all usable buildings? Cheap drones as a defensive weapon make war way more costly to the aggressor.
No, they made war expensive for people that are used to overwhelmingly superior but expensive military force. Drones are perfectly capable (even excel at) surgical strikes, and if the enemy destroys a $1,000 drone with a $100,000 missile, it's still a win for the drone.