Sounds like some botch-up in planning : "Works at West Footscray station involve realigning regional, suburban and freight tracks
During planning for the Regional Rail Link, it was publicly stated that they were in communication with the design team for Melbourne Metro. Why then do newly completed regional tracks (ie RRL) and newly moved suburban tracks (paid for by RRL) need realigning ? No wonder infrastructure costs so much in Victoria.
It is quite easy to see that without a turnback at this location, Melbourne Metro would be unbalanced. There is currently a 10-minute daytime and weekend frequency on the Dandenong line, but only a 20 minute frequency from West Footscray to Watergardens. A turnback here provides timetable flexibility, and would match a similar facility at Oakleigh should additional services to the west start, such as to the Airport.
For regional users like myself arriving at Footscray after 9 am, there is only a 20-minute frequency from Footscray into the City Loop. We no longer have access to the other Northern group city loop lines for transfer at North Melbourne. So a 10-minute daytime frequency from the loop as far as West Footscray would provide more options for both regional passengers. Footscray is also the 8th busiest station for transfers from buses, with 1700 passengers per day (2013/14), and probably more now that RRL works are finished. From about 3:30 pm until nearly 5:00 pm, there are a lot of 12 minute gaps between trains from the city loop to Footscray. These trains are extremely crowded until large numbers of passengers leave at Footscray, most of whom transfer to buses and some to regional trains.
A 10-minute daytime frequency as far as Watergardens is probably not justified on patronage, and would delay regional trains.