Not stopping means even people intending to travel to Shrewsbury, Hereford or Cardiff can't use the service. It doesn't just affect people in Wilmslow trying to get to those destinations. The station car park at Wilmslow is often full, as it's a local hub for regional and Intercity services.
Trying to get from Wilmslow to Manchester by bus involves a change at either Wythenshawe or Handforth Dean. As the buses to both Wythenshawe and Handforth Dean are only hourly, it might mean connections don't work well. And God forbid if someone from Knutsford had planned to travel to Cardiff on a strike day on the basis they could get a direct bus to Wilmslow station. It would take them a couple of hours to get to Manchester using other public transport.
Pick up only in the Crewe direction caters for people in Wilmslow going to Shrewsbury, Hereford and Cardiff. The only flow it prevents using the train is Manchester to Wilmslow which, seems right given the TfW train is the only way to get to the places you mention.
No doubt Wilmslow gets a huge number of people using it, as a regular user of the Marches trains I know how many get on and off.
Likewise there is no easy way to say that any flow should not be catered for, but even 1 change of bus is better for the Wilmslow to Manchester flow than leaving people unable to get on the train because so many passengers are doing Manchester to Wilmslow.
In an ideal world all the 158s not being used by Northern could be borrowed by TfW, but that doesn't work for so many reasons. So TfW ends up with 2 carriage trains trying to fit the normal TfW flow plus all the passengers that would have been on Northern or Avanti between Manchester and Wilmslow. I think you can see why there is no Manchester to Wilmslow option in a strike.
