It is a prime example of sunk cost (and the sunk cost fallacy), but it doesn't explain why they're only raising prices now, rather than back in October when the

It is a prime example of sunk cost (and the sunk cost fallacy), but it doesn't explain why they're only raising prices now, rather than back in October when they locked in the agreement. The linked-to WSJ article explains that Starbucks will be paying 'more than their competitors' for coffee, but they're still not paying 'more for coffee' than they expected to. That's the nature of a forward purchase agreement.