DQ is sandwiched between Karjat-CSMT and Titwala-CSMT local trains when travels in up direction so halt is not possible in upward direction.
Now talking about downward direction if you have noticed 5 PM Ambarnath local do not halt at Byculla, Kurla, Ghatkopar just to ensure highest clearance to be given to DQ and Howrah Duranto running behind it.
For us it is just 1 or 2 min halt but for actual operations they need to reduce speed to halt at platform and again pick up the speed and lot of time is...
more... required for all of this
Again as highlighted by other users DQ is meant for end to end commuters