I sometimes dont't like that celebrities advertise a project, they were usually paid to do so, and that does not reflect in the project itself, now if a celebrity advertise on its own, due to actually liking the project, then that is different, but any celebrity will do that, because they have a lot to gain by charging the project itself.
but celebrities have a huge amount of followers/fan community. if only some of them see, oh my celebrity is advertising this project, they will probably hop into the project ^^ = new investor
