Actually, the returns can be larger on a film made with a smaller budget.
What I see happening is that if a film has a larger budget, the harder the climb to profits. Some films can do this, like Man of Steel. Other films, like The Lone Ranger, can't do this, which can be calamitous for a studio. Walt Disney's stock has declined with the news that their latest film is a John Carter in the making.
For a film to succeed, it must be able to transcend cultural barriers, have good word of mouth, and have a hook to get people into the chairs.