Your analogy between Citibank and Coinbase is telling. Citibank is, well, a bank. Coinbase is a currency exchange, and more analogous to those Forex booths you

Your analogy between Citibank and Coinbase is telling. Citibank is, well, a bank. Coinbase is a currency exchange, and more analogous to those Forex booths you see in airports. There are Bitcoin banks, but putting your Bitcoin into a bank loses the decentralization benefits. Admittedly holding onto your own BTC requires more security than many people are capable of implementing, but better and better solutions are being created to solve this problem.