He isn't as marketable as Roman.
The marketable excuse is moot at this stage. It held up in January 2015 when the question was still unanswered. Not so much in June 19, 2016. They've marketed Roman for over two years and attendance and ratings have only declined more drastically than they were before hand. He's on every commercial. Hes on RAWs intro video to begin and end it. Every talkshow. On nearly every poster. This is even the first time I can recall the damn champion being on the MITB Poster with....the MITB briefcase. If it was possible and they thought it'd get him over, he'd win the MITB, lose the title to Seth tonight, and cash in immediately after.
They've marketed and pushed Roman harder than anyone on the roster, and he hasn't done jack shit with it. There's zero proof he's more marketable than the likes of 90% of the upper card if they received the same two year push. He ain't The Rock or Hulk Hogan. It takes more to be marketable than one finding a guy hot, exotic, or having "the look" which is partially why interest is approaching an all time low.