So the quiz is titled "Top box office stars since 2000" which is a quantifiable metric. Then the subtitle says as voted on by movie exhibitors. If the answers are the result of a poll, then it isn't really a box office quiz, now is it?
I was wondering the exact same thing. If it's based on votes, then isn't it more like... the ten stars popularly perceived to be the biggest box office draws?
This is from the linked source: "The Top 10 Poll, which appeared annually in Quigley's International Motion Picture Almanac has long been regarded as one of the most reliable barometers of a movie star's box-office power, as film exhibitors base their decisions on one economic criterion: those stars who will bring patrons into their theaters."
The Tranformers series Shia starred in was a ubiquitous box office success. That's what this quiz is asking for - who starred in the most profitable movies for the listed years i.e. which stars brought in the most money. In Shia's case it just happened it was the movies and not the star power that brought in the money.
I feel similarly about Will Ferrell, Steve Carell, and Melissa McCarthy. I don't mind some of Ada Sandler's older work though, so for my list I would take him off and replace him with Sacha Baron Cohen. I couldn't laugh at any of his "comedy" if my life depended on it.
Ferrell
Carell
Sandler
McCarthy
Stiller is close to being in this group, but unlike those listed above he can occasionally make me laugh.