It stops at DMM and BPQ for crew change. While NGP can fulfill the requirements, there are 2 reasons why BPQ is also provided.
Change of zone - Usually one a train moves from one zone into another, the crew is changed at the earliest possible station. BPQ is the transfer point for SCR to CR, and DMM is the transfer point for SCR to SWR. And since these stations are already equipped with the necessary facilities, crew change is done here.
Crew work time...
more... - Usually the crew is limited to a maximum of 6 hours per shift. And most of the time 4-6 hour shifts are the norm . For the south bound trains, especially the SF trains towards BZA, the BZA NGP stretch takes about 10 hours which is too long for a single crew to handle. This makes BPQ a very convenient point for a crew change as it is about 7 hrs from BZA and also a zone change point.