One bullet from one drone, and the thing is a puff. It's more expensive to build than a drone? Why does this make sense?
One bullet may not be enough unless it hit the flight computer.
When the navy shoots bullets at a incoming projectile, they pretty much create a wall of lead (Phalanx).
Even if you could shoot one bullet, one bullet could go through it and into the window of a high rise office building.
The answer to why it makes sense in that case, is that there are so few other viable alternatives to deal with swarms of drones (none currently).
There are - if the AF was functional. Any viable alternative has to have the same form - low price, and distributed - from none of the Military contractors.
Bullets are cheap, but I don't see that solution working in urban environments.