Under Site setting > Privacy you can decide how your favorites are displayed to everyone else.
I guess a tactic would be to favorite tons of stuff out there and then have them private to get traffic to your page, and I wouldn't look past it if there are those who do this, but I believe a lot of people just hide them because they don't want everyone to see their favorites for various reasons or possibly to have their page focus on their art and posts when someone visits their profile instead of other artists pictures.