It always seems to have a relatively weak case whenever TfGM examine it. I think it boils down to lack of real population density after Hale to sustain a frequent service until you're at Knutsford itself.
Mobberley is a very large village by area and the issue is the station is at the far extreme so for some Mobberley residents it's 1.5 miles to the station but there's also places of employment in Knutsford also 1.5 miles away, so many people in Mobberley aren't going to get a train to a job in Knutsford. Due to how spread out the village is that increases the likelihood of passengers using the station having bikes, something Metrolink doesn't really have a solution for.
I'm pretty sure TfGM actually proposed relocating Mobberley station in their tram-train proposal to move it near where the rail line crosses Broad Oak Lane and then putting installing CCTV, 6 ticket machines, a lot of cycle storage and a lot of parking to make it a Park & Ride station, which was one of the reasons the whole proposal became unaffordable.
There is still the Preston service though, I think? Perhaps some stops should be inserted in it.
I think that's already happening in the absence of the second hourly stopper to Wigan. There's also some stations on that section which the Liverpool to Crewe via Manchester service calls at, obviously that's no good if people want to travel to Wigan but is just as good as any other service for going in to Liverpool.