Imagine my yearly pay will be 150K at Amazon or 200K somewhere else.
Amazon stock could go up, and my pay in my second year could be 250K, in which case I am making more by being at Amazon.
Or it could stay the same or go down, in which case my pay in my second year would be <= 200K, but in that case I can just ditch Amazon for another company to bring my comp back to market levels.