Two things. First, they will in fact pick and choose which parts to abide by, knowing fully that the grievance and arbitration process will take years. Sadly at the regional FO level we are talking the difference between poverty line and not. Many people can't grieve and wait and still put food on the table.
It doesn't take real unions years to settle grievances. The IBT is absolutely dismal when it comes to enforcing their contract. How long has it taken for them to grieve the definition of a seat? The IBT apologists will blame it on the arbitrator but anyone with half a brain can see through the incompetence of the IBT.