Because, as it turns out, using cryptocurrency as currency is too expensive. The exchanges let you "trade" and then settle themselves in way fewer transactions,

Because, as it turns out, using cryptocurrency as currency is too expensive. The exchanges let you "trade" and then settle themselves in way fewer transactions, so you don't have to pay nearly as much in fees. It's the same reason we keep our money in banks instead of everyone owning a Fed terminal and requesting ACH pulls.