The lion habitat was frequently ranked as one of the best free attractions on the Las Vegas Strip. It seemed to be very popular, attracting a nice crowd whenever the lions were there and active.
Despite the popularity, I'm guessing the habitat wasn't a money-maker for MGM, as many of the visitors were families with children not old enough to gamble.
The habitat received some bad publicity at the end of 2010 when a video surfaced of a lion attacking one of its handlers. Not sure if that led to the decision to close the attraction, but it couldn't have helped.
