There are 3 types of advertisers, 1. People who advertise their own/somebody elses anims on anims made by other animators. 2. People who advertise their other anims on their own anims. 3. People who advertise fanart for somebody made by them onto the animation that somebody who is the one they made the fanart for. 1st kind is just view begging. 2nd kind is showing the viewers an animation that it is based off of an earlier animation made by them (example. Remakes) 3rd kind is just fanart.