Police arrests also require preparation. To put it in terms more understandable to the average person—it requires an appointment.
The kind of "one command, everyone assembles" scenario applies to the military or SWAT teams, but not to criminal police.
Everyday criminal police are either traveling, completing assignments, buried in office computers writing reports, filling out forms, and adding supplementary materials, or attending meetings, listening to directions from superiors—apart from that, it's evident that, as humans, they also need rest.
If you call people without scheduling... of course, given Jiang Yuan's current status, issuing an order to assemble hundreds of people is not a problem. However, being in such a position of responsibility, if he has the authority to issue orders, he must also consider that one command increases the workload for everyone involved.
