Disney made it very clear that they will be killing off both the Marvel: Avengers Alliance and its sequel. According to Disney, they made the decision so that they could spend their time on something better.
It made sense that they wanted to kill off the game. The sequel of the game did not do as well as Disney thought it would and the game was just a waste of their time. However, the fans think that Disney will not just give up on the Avengers so soon. Some fans have speculated that Disney might have taken off the game so that they can work on a totally new Avengers game.
Of course, Disney has never said anything that might indicate that that is what they are working on so it is best to take it with a pinch of salt.
Disney has been making some questionable decision when it comes to some of their games. The fans are still furious that they decided to ax the Disney Infiniti game.