And in turn, why would market rent for your area be N instead of N-$500 (or N plus discount matching), if that discount is generally available? If everyone gets the $500 Amazon discount, then everybody has the switching cost problem, and so landlords would want to match what the market is actually willing to pay, not what it looks like they're paying on paper. This is basically the same scenario as early termination fees - when cell phone companies decided to increase the switching cost, other cell phone companies said they'd eat that increase in switching cost just to unlock locked-in customers that they couldn't reach.
And ultimately all of these mechanisms are annoying and fiddly mental overhead, but could purchasers band together and join an organization that negotiates on their behalf, organizes boycotts, etc. for a relatively small fee?