As someone who used to work at Coinbase, hopefully I can shed some light on this.
First of all, Bitcoin should not be seen primarily as a currency, but as a protocol. Therefore, bitcoin does not need to increase in value for it to be successful, and in the long term the price is irrelevant. Bitcoin can be used as a medium of exchange without regard to the price, and many people at Coinbase believe in this future (rather than bitcoin becoming a widely used currency held directly by end users, at least in the near future).
Secondly, many people at Coinbase believe deeply in the decentralized (and potentially anonymous/privacy-focused) aspects of using bitcoin as a currency (myself included). However, bitcoin cannot be successful as a currency unless it is easy to exchange between bitcoin and your local currency, and bitcoin won't gain worldwide acceptance until it is easy to (a) exchange bitcoin and (b) spend bitcoin. Therefore, Coinbase's primary goal is to make buying and selling bitcoin as easy as possible, so that we can enable a future where financial privacy is optional (versus today, where it is basically inescapable).