According to me; whats are the possibilities-
1) Crypto is being purge by Youtube.
2) Attract by some kind of group intentionally.
3) Attract from Scam Coins (Since good YouTubers telling the true story).
4) Wrong YouTube Algorithm.
5) Lots of Fake ICO, Crypto Exchange related videos on YouTube.
Not all crypto related videos on YouTube are banned and deleted by youtube. I think they delete some scam ico videos and exchange like you said. Because until now i see many videos related in crypto but this is tutorial, educational, and some trading analysis.