It turns out that security was the domain where Coinbase needed expertise. Selling something and taking a commission is not exactly the nosebleed seats of high

It turns out that security was the domain where Coinbase needed expertise. Selling something and taking a commission is not exactly the nosebleed seats of high finance. Lots of people with expertise in setting up a web site, and enough finance to run a business, could have become Bitcoin markets. Indeed, a lot of them did. Most of them got hacked, sooner or later, because protecting billions of dollars of value from adversarial forces is very, very difficult. Coinbase didn't. Security is the hard part.