They (DHL) should have settled up in SAC or Mather.
MHR doesn't even have a full (1800 RVR) Cat I approach though they'd probably have room for the facility.
By SAC do you mean SMF or somewhere else? The sort facility at RIV is a very large truck sort as well as the air sort. I'm not sure that SMF would have had the room.
I also think that they wanted it closer to (i.e. in) the LA Basin for truck access to LAX. Just guessing on that, though, as they load a lot of cans into trucks that are labeled for international belly freight out of LAX.