Whenever I have to judge potential of a movie, I ask 4 or 5 people around me. Each of those people fits into a different type of movie viewer and that gives me a good idea.
Shivaay's trailer hype was mostly just in media. People generally said that seems like typical movie where hero beats everyone.
So that initial hype maybe wasn't there.
Then music wasn't successful.
Ajay has very limited potential outside of Rohit Shetty movies. And he wasn't enough to get big crowds to see the movie.
Finally, content was just average for audience, while the multiplex audience was only interested in ADHM.