Did any established math youtubers, like numberphile, standup math, veritasium or singing banana enter?
The exposition contest was designed to give them a little push and get eyeballs on their content, so they've got an actual chance to be noticed, no matter if they win.
An established YouTuber entering it would have taken attention away from those new people.
So the spirit of the contest excludes those YouTubers.
[1] https://assetstore.unity.com/packages/tools/particles-effect...