I posted this on another thread about tips for this, but I'll answer here too. I was having the same issue until I tried changing up my Sims traits a little. Natural Born Performer seemed to help with this a good bit. The trait's description says that it helps draw a crowd, and it seemed to help here too. Irresistible seems to help too since it makes other Sims want to socialize with you. I haven't done a lot of testing on it, but having one or both seem to help getting the 10 watchers for the Legacy statue.