It's more like DL found out that A4A was a democracy, and wasn't able to simply get their way on everything because Richard sayeth so...
Now, instead of spending $5M a year for A4A to do the lobbying on their behalf, DL will spend at least that much trying to do their own lobbying, and it's probably not going to work out any better for them as a single entity.
But hey, other airlines have tried to go it alone. Braniff v1.0 did. Worked out well for them in the end.
Welcome to the dark side. Just ignore and move on.