That's a good questions, The reason being smaller channels are less known and have less to offer, seeing as most people don't have the entire day to browse through videos. Nor does your mind work in a manner that boredom won't set in. That being said, this is the normal reason smaller channels get looked over with add placement. I'm sure you've already read the science behind the first five seconds of any pitch is where are person will continue to hold interest or will lose interest. Those adds factor into that essentially.