This was always my issue with the Ultimate version FF.
In 616, Ben was an astronaut, and despite being Reed's unofficial bodyguard for their entire lives, he was still pretty intelligent on his own and could contribute a little more to team besides being a brute. Also, he had good reason to be a part of the expedition that led to their powers, as he piloted he ship.
In Ultimate, he was just Reed's jock friend who happened to tag along for the N-Zone portal demonstration.
And with them altering that into a teleportation experiment in the new film, it now makes even less since for him to tag along.