Could cause conflict for players who aren't max level (100) and haven't unlocked all the weapons
also if you still have even 1 ammo for your preferred weapon and you call a supply drop, you will get ammo for the weapon you had, and it won't be replaced. However if we were to allow players to choose a preset of weapons, some players may not know how to change the weapon preset leading to them replacing their preferred weapon with something inferior (sawnoff to a normal shotgun for example)
The only situation this suggestion is useful in is if you have completely depleted your current ammo (jailed too many times, confiscated weapons gone, or you used all your ammo up) in which I agree, it could save us time, still I see alot of gaps and holes that this implementation would bring, -1