Scheduling pretty much does what they want with SC - yes, there are some restrictions but there is a lot more going on than we see. Sometimes pilots have rest issues that prevent SC, sometimes they are going into Golden Days off so they can't be used, sometimes because they are coming off a X day they can't start SC until 10am, so they need you for earlier. Etc etc.

Every time I've called to ask why did X happen or Y, there is always a reasonable answer that leaves me with my original assignment.