This seems like a simple enough tip, yes? Then why don’t you have custom thumbnails on your YouTube page?
Admit it, you don’t have them. Don’t be ashamed, you are definitely not alone. However, this is a fairly simple task that could easily be completed in an afternoon. Do you have an intern? Even better. Give them a chance to flex their Photoshop skills, and put them on the project. Have them take a screenshot of the page before and after they upload the screenshots. They can use this in their portfolio!
Alright, we all agree this is an extremely easy task? So go take care of it!