It's not about that. It's about who Affleck is in his career right now. Do you guys really think he'll do the RDJ and play this character six times?
Hell no, he's not. He has too many interests as a director to play this character six times at this point in his career. He just won't do it.
WB is not building a cinematic universe in the way fans want. I still contend that they're just doing a trilogy that began as a Superman trilogy but now has been converted into a trilogy about how the three greatest superheros came together.
Of course, this is my opinion, but this is my gut feeling on what WB's doing.