Well, frankly, it's hard to imagine why he would take part in such a dreadful production. Except, of course, the dough. One would thing Stewart wouldn't sell himself to third rate screenwriters and producers. Lure of money and fame did it, however. A shame.
You might want to read or listen to interviews with him to see what he thinks. He can speak for himself. You don't have to speak for him. Because you can't get inside his head.