The British Transport Police (BTP) base their coverage of the Tube network (i.e., where they send their personnel, and when) on "Lost Customer Hours" (LCHs).
LCHs are a company measure of how many hours are lost due to incidents on the line. At busier times, when more "customers" are on the train, a delay results in more LCHs than at quieter times.
Therefore, one incident of in the peak could result in thousands of LCHs, whereas several incidents in the early evening or morning, causing much longer issues may result in fewer issues and perhaps not get the priority response they should have.
This setup means the police are basing their response not on where crime is highest, and where passengers and staff might need most support, but where it disrupts the service most. Essentially they are policing for the bosses, not for the workers or passengers.