How will cap stop phoenix from destroying worlds? If Cap got Hope, Phoenix will still go towards hope and destroying worlds while making the journey. Even moving Hope away from earth would not stop Phoenix from destroying other worlds.
And it was not Scott that made hope run away it was Wolverine. When he tried to assassinate hope.
And at the end of X-sanction when Hope first manifested Phoenix powers in front of Scott and Cable, Cable from the future he showed Scott, that the avengers should be stopped in trying to get hope or the future is doomed. I believe Scott is acting on that? But then again there was also Bishop, reasoning hope will cost the destruction of the world. Which future is right? I wonder.