it's not about crypto. It's about human nature of mankind - most people with balls and ability to steal will steal.
Bernie Madoff did scam people from $60 bln (if we cut of fake ROI promises, it was still around $30 bln for deposits).
The problem of cryptocurrencies that you can easily get away with scams/theft (you don't need as big balls as IRL thiefs).
And you have tons of inexperienced people with relative wealth.