A drone can be used for more than a singular purpose. There might be more efficient ways to kill someone we already know like you said but what if we don't know them yet?
What if they don't exist yet?
Imagine you have a crowd and there is one violent person inside it, how would you immobilize such a person without harming the others?
Why pay for their pension years after they have retired?
Why pay for their healthcare, training, damage, etc?
Even the most insidious state relies on its citizenry to some extent. You're not ruling anything if your people are constantly in revolt, or if they're all dead.
Yes, there is a money problem for employing enough cops.
Reference - India.
https://en.m.wikipedia.org/wiki/List_of_countries_and_depend...
In an ideal future, autonomous drones would make less mistakes since they don't feel threatened or care about dying. They won't kill someone just because it looked threatening. They won't turn off the body cam because of reasons. They will have a more accurate aim and will be more trained since training doesn't cost anything for them. You can invest the other funds in improving rehabilitation or de-escalation services.
Hmm...a gun?
Humans aren't good in stressful situations and their aim isn't great. A ground view isn't necessarily helpful in situation where the criminal might be inside the group ring.
Also sounds like the cost for those snipers would be pretty high than manufacturing few drones to lock in a target and swarm under their head.
Cost of drones is only going to decrease while the cost of sustaining human life remains more or less the same if not increase.
A drone is $30k