But that's my point...
The police force for example, at least in an Altis Life server, it's always hard to find someone who is willing to be a cop, and take the role of being the cop rather serious, or at least serious enough that they're not sat there randomly tasing civilians, or speeding around just because they can't be bothered to adhere to speed limits.
To build an entire police force with those people may take literally thousands of people that join your server. Some days, you're going to log in and find absolutely no police officers online, and then as you say, players can just exploit it and rob everyone with no consequences.
The video details that the police force has a structure to it... I presume by this, it means there are different branches where players are assigned different cases, or there are ranks that you progress through and have different roles to play as while you are that role...
But I have to question that... what if, say the sergeant rank, has players sit behind a desk, and micro-manage other players? Sure, it's a nice role to be "the boss" for a bit, but it'd get boring. What happens when no players want to fill that role, or players only in that role are online? Does the police force collapse as a result?
Ultimately, I think NPCs would work extremely well in this as "placeholders". It wouldn't take much away from the immersion if NPCs took part in some of the jobs to keep the system going. Sure, you can't have a friendly conversation with them, but maybe all they need to be able to do is say "Hey, how's it going?" if they pass you on the street... or even just give you a friendly nod as you walk by. The Bank would need to have some form of security in place, otherwise what stops absolutely everyone from robbing it as soon as the last police officer logs off for the day?
If there's a fire service, and houses that can be set on fire by an arsonist (I have no idea, I haven't seen anything on this), who puts the fire out? Does the fire just spread and burn the entire city to the ground if there aren't any Fire service online?
As cool as it may be, being a police officer and cruising around with your partner (your friend) to bust bad guys. If you're playing the game alone because they're offline or away or whatever, it may make the difference to your experience if you have a simple NPC keeping you company coming out with witty one-liners everyone once in a while as you make an arrest, or even have the NPCs mentor you as you're learning to be a police officer.
In no way am I saying "Make NPCs the focal point of interaction" for this game, I'm simply suggesting to the community, it's worth considering their involvement in the finished product, and how they can greatly add to the game.