Who knows? Maybe Steve asked him to? Maybe he feels that somebody needs to be Captain America, that it's more important that there is a Captain America than that there is a Falcon. Captain America is bigger than the guy wearing the costume.
Who knows? Story's not even printed yet.
Also, you've been reading comics longer than this, you know that nobody is giving up anything, just setting it aside for a few story arcs.
Preview art shows him still having the wings.