there are a few reasons. First, celebrities have a lot of influence. Their fans look up to them and often want to emulate their style. So, when a celebrity endorses a product, their fans are more likely to buy it. Secondly, celebrities are often paid handsomely to endorse products. This was especially true for A-list celebrities who can command millions of dollars for an endorsement deal. For them, it is simply good business. Finally!! some celebrities genuinely believe in the products they endorse.They may have been using the products long before they were approached to endorse it publicly..