Why? Let's say that this robbed unit is used for a flight that's international and crew is at risk of timing out. Would you, as Delta, rather risk a longer flight cancel with 3x the revenue as DL1908? Or would you delay DL1908 for 4 hours, take that hit, but run your international flight.

There's dozens of scenarios that make perfect business sense. Now, that doesn't mean it doesn't absolutely suck. But it doesn't boggle the mind at all.