There were still a lot of people that didn't know Man of Steel was a Superman movie at the time.
Just because it was marketed, and made some money, doesn't mean that everyone knew it was a Superman movie.
In fact, as I said, the majority of people I knew and spoke to, didn't know it was a Superman movie. Regardless of your numbers.
Edit: And the people I did know at the time, that knew it was a Superman film, all saw it more than once. Hell, I saw it 3 times, which was an abnormally large number for me to see a movie in theaters (at the time).