-Security concerns: Fear of getting hacked or scammed.
Your bank accounts can be hacked. Phishing sites can be used to fake bank websites or cryptocurrency project or exchange websites.
-The volatile nature of cryptocurrencies: Losing funds due to the volatile nature of cryptocurrencies.
Cryptocurrencies are volatile but your money is not safe in bank account. The number represents your account balance can become valueless if that bank files for a bankruptcy. You will not be able to withdraw your fiat from a bankrupted bank.
-Regulatory concerns.
Regulations can be changed for both traditional banks, cryptocurrency projects, cryptocurrency exchanges. Don't over worry about regulations.