Most of the states that are party to this suit host a huge presence by either US or AA. Some such as Florida are ensuring they won't loss status with the combined entity. Others such as AZ want to make sure the get some $ out of this for all the lost tax revenue off of employees that re-locate with HQ and the possible PHX downsizing. Texas wants to make sure all the small markets that are AA strong, don't lose a single flight or un-nessecary fare increase.
The Feds are in this because someone paid them, simple as that. Probably UA and DL worried about the amount of TATL market share the combined US/AA would carry out of JFK and PHL.
The Feds are in this because someone paid them, simple as that. Probably UA and DL worried about the amount of TATL market share the combined US/AA would carry out of JFK and PHL.