DFO in Mentone is so cheaply constructed. It's just one big concrete slab shelled by cheap walls and roofing. The car park asphalt is also the cheap stuff.
This thing brings consumers which attracts more businesses which brings more consumers which attracts more businesses etc, etc. The car park is always full, though not as chronic as Chadstone Shopping Centre which has much more parking.
Like Chadstone SC and DFO in Docklands, DFO Mentone should start expanding by building underground, but the easier, cheaper and greedier option is to simply aquire the land next door. I'm sure DFO Mentone is a cashcow and they have the money to expand it underground, but they appear to have met very little resistance with their current plans.