And they obviously believe the price will keep going up, because they're a bitcoin business, and believe in bitcoin. If the price stops going up, their company will fail anyway.

And finally, perhaps you noticed that coinbase is processing thousands of bitcoin purchases now. So I'd say, with all that data, it's not actually that risky for them. If the price starts going down, they'll know it first, because they'll be the ones making the purchases. :P