Of course every generalization is wrong but a not so little part of the crypto community seems very interested in avoiding taxation, money laundering and buying illegal stuff without detection.
Actually, I was flagged over $6000 deposit over the sale of a car.
The IRS gives rewards to bank employees if they report (successful conviction) any suspicious behavior.
I still don't know why I was flaggged. Probally because I had long hair at the time?
I had a bunch of sleepless nights over that incident, and a bunch of emails back and forth.
Internet file sharing is older than you think. Together with remote terminal access (TELNET), file transfer (FTP) is one of the oldest Internet protocols. When file transfer over the Internet first started, that is, when the Internet itself started, it was not "illegal".