Contingencies. In every business, especially a large corporate with common issues, like mechanical breakdowns, bad weather, etc., one must have plans. You plan your endeavors and then work your plan. Customer service was once a pillar of business. It is no longer. If you think this particular “issue” suddenly reared its head and management was caught flatfooted, I have a beach property to sell you.
They do have contingency plans.
Every major airline has extra crews on call at their major hubs, ready to send whenever an additional fresh crew is needed.
Kentucky isn’t a major hub. They don’t have a spare set of crew there. Chicago is a major hub. They had to send the crew from Chicago to Kentucky cause something happened. That’s the contingency plan.