Unfortunately, these days you don't even need to have anything like p2p to scam people. You could have a website that is looking "legit" but in reality, would be a ponzi scheme.

Most commonly, for many years people put their money into many exchanges, and exchanges didn't protect themselves carefully and got "hacked", we can't really know if they were hacked or they just stole our money but the result were the same.

This means that we saw a lot of money put their money as a whole, the "business" worked as intended for many years, but then one day suddenly they just stopped and took our money and left. That’s the scary part and it could happen and that type of scam is horrible.