I've actually seen a lot of the opposite on Chinese media. I see a lot of SWATs using ARs and SMGs whereas only office workers, post guards, and civilian-clothed operators such as the DEAs use pistols. Then there are patrol officers who also are seen holding ARs, SMGs, and even shotguns. As much as PAPs are used, they are not everywhere all the time.
Think about the videos you are seen , where were they filmed ? in training, on a firing range.
Think where you ever saw a video of Chinese SWAT been deployed on a suspect with a gun , and think how many PAP are deployed against a armed suspect.
The police force in China don't , and not meant to handle armed threat with a gun, if they do ,it's by accident and not intention, even if the drug busts are carried out with PAP as it's main firepower.
On another point , and here lies the problem really, there is a reason that you see many SWAT around the world not using SMG anymore ,it a product of a by gone era, if given a choice, buying a rifle or SMG , most application will choose a rifle.
If the threat has a gun , you want a rifle , and if the threat doesn't then a handgun is enough .
The only advantage a SMG has over the rifle that is lighter , and shorter , and more easily controlled in full auto.
The first 2 are compromises worth taking for a bigger punch, and the latter are a none factor as police applications don't use the full auto any way , all of videos you see them doing it is in the firing range.
SMG, it's name says it all , it a sub-machine gun , and the machine gun referenced here is ones water cooled like Maxims during ww1.
It came into existence to provide full auto fire power in a time fully automatic rifle for single person use didn't exist.
Post war just about every army stopped issuing SMG in it's battle order as a standard equipment , and post 1990s when short barrel rifles become more common SMG lost the last advantage of been shorter then what a rifle could be, in most cases , where you can fit a SMG , you can fit a rifle.
On the other end , the main problem with handgun beside the lack of firepower , is training .
It takes much much more training to shoot a handgun under stress compare due to lack of support from shoulder.
It takes much less time for someone to be trained to use a SMG well compared to a hand gun , but the same holds true for a rifle.
So the training advantage of SMG compared to a handgun , rifles has it too.
Here where the conversion kit come into the picture, to solve the training issue.
Basically , if you see any unit armed with SMG in any country , it is most likely some other limitation are in work here ,for example they can't buy a rifle ,or an older army SMG is leaving the inventory so they can get them for free.
Other then that unless you are a special service branch that need to hide a gun under the suit , you would get a handgun or a rifle.