Pure ignorance. You and I have two very different definitions of "high security". I wouldn't consider a bank transaction secure at all, and
banks are moving towards cryptocurrency as a result. This argument of insecurity stems from ignorance. Cryptocurrency, and the blockchain in general, are implementation dependent but generally highly secure when built well. Far more secure than anything your bank or broker does today.
If someone steals your money now there is no trace. For all you know your money at your broker is gone and you've been trading at a bucket. Banks aren't required to keep enough capital on hand to stop a bank run - what makes you feel like your money is safe? The government? HA. HAHA. HAHAHAHA. Great joke - they can't even manage their own money. Tariff man has made sure of that.
There are no "virtual cryptocurrency banks". You store your coins in a wallet. The blockchain is used for transaction verification. The weaknesses come from:
1. When you
do transfer them to an exchange for management (bad idea)
2. The algorithm underlying transaction verification is weak (look up 51% attack)
(1) Requires you to move coins from your wallet (safe and secure if it's on a hardware key) to an exchange wallet that they control (insecure because you do not control it, it's implementation, or location). Obviously this is bad and a risk you must undertake to trade coin.
When
Proof of Stake becomes wide-spread the likelihood of (2) goes down significantly. The idea of a "cryptocurrency bank is wrong anyway. Cryptocurrencies will never have banks. There is no reason. Wallets are all you need, and the blockchain forms the "cash security" a bank usually supplies.
Our world will move towards cryptocurrencies. They are the future. Fiat won't be around for much longer (in the geologic timescale sense), and as a result neither will banks. Governments are rushing to figure out a way to stop the mass adoption of cryptographically secure money because they can't tax it.