There is certainly almost no justifiable reason for why an individual with many years of performing in motion pictures or television programs would be qualified to give us sound advice. At the same time, people do listen to celebrities, even if there is no reason to do so. Celebrities serve the role of trendsetters.
People absolutely listen to celebrities more than non-celebrities (unless the non-celebs are super high profile). We read about what they eat, wear, how they sleep, where they shop for groceries, so most folks are fascinated with celebrities and sports stars. Good on Yao Ming for helping decrease shark fin soup consumption, and hopefully finning as well. Celebs/sports stars have a lot of media coverage and a lot of public influence.
Former NBA players Yao Ming's campaign against shark fin soup is a good example of a celebrity using their notoriety for a worthwhile causes. People admire and like celebrities. Because these celebrities spend so much time in the public eye, people feel they know them and have an attachment to them.
People listen to celebrieties more than they listen to actual experts in a field. This is why so many people listen to celebrities who have tried things like vaginal steaming and other similar ideas , even though scientific evidence shows that this is actually dangerous and has no health benefits.