I know you know this, but I think a small clarification has to be made here.
No individual pilot can file a "grievance" themselves. They are disputes at that point. The union will then discuss them with the company, and if there is a violation they can not resolve, they union will file a grievance and that's where the process starts. Most disputes are handled at this level and they never escalate to a grievance.

So it's not that the union "won't" file anything, it's that the pilots have to send the disputes first. MEC grievances are different but I'm not sure if they see this as a MEC grievance.

I've heard from a somewhat credible source that the issue is that pilots don't file disputes, they just go to facebook or APC and complain about things.