Unfortunately for Pinnacle pilots, their management signed a bad contract. They had to maintain a completion factor over 95% during 3 of the last 6 months. When they didn't, Delta canceled their flying. It's unfortunate that Delta management didn't give Pinnacle any "spool up" time to learn the ropes and adjust to the system, but it didn't happen. Most likely Pinnacle management overpromised and then underdelivered.
My totally uninformed speculation is that this was all a plan to put pressure on ASA/SkyWest Inc. to finish the ASA pilots' contract. The plan worked, ASA pilots gave up a few of their demands, ASA management gave up a little and once they got a contract, there really was no use for Pinnacle. Delta knew that ASA/SkyWest Inc. must have 80% of the ATL flying, and with the projected growth for Pinnacle as well as the continued loss of aircraft to retirement at ASA, they were going to fall way off that mark. So Delta could either move Pinnacle to another hub and somehow get more aircraft for ASA/SkyWest, or cancel Pinnacle outright to comply with the protections that Jerry Atkin wrote into his contract. They picked the less costly route.
Unfortunately for Pinnacle pilots, you all are caught in the middle. You didn't sign the deal with Delta, nor do you really have any control over completion factor or A14. While you may have great numbers this month, one airplane going down for MX hugely affects your operation when you only have 10.
The good news is that the 900s are in huge demand right now and most likely you will find homes for those aircraft. Don't let it affect your goals for your contract negotiations... ASA lost countless growth opportunities during their contract negotiations and still came out with an above-average contract. If you stay strong and unified good things will happen.