They do this because Polar (Bobb, or more correctly Robin) has indicated by words as well as actions that he does not want to merge. While I would love to blame the company for this one, it is simply not true. If you are a Polar pilot and have a problem with this action then I suggest you call Bobb.
This is only the beggining of Plan B. Expect much more Atlas scheduled flying. Expect a grievance or lawsuit by the company against ALPOlar soon for non-compliance.
Winning the battles (ARbitration) while losing the war (integration) was NOT a good idea.