The United Club card is the premium version of the United Explorer card. However until now I’ve never seen it offer any bonus miles for signing up. In the past Chase has felt that the card benefits were rich enough that they didn’t need to offer a signup bonus for the card. But for a limited time only you can get 50,000 bonus miles for spending $3,000 within 3 months on the card!
probably because delta recently added a signup bonus to the delta reserve, and citi aa executive has had for a long time (maybe forever, don't know), therefore they had to get back into the game so to speak.