When they do this, it's usually a shittier offer than it sounds. They're not offering cash, but value in tickets, which has an expiration a short time in the future, and can only be applied to certain flights.

It'd be interesting to see statistics on how often these offers are even redeemed.

The few times I've taken the offer, the tickets were good for a year. But for someone who doesn't fly a lot, that is a relatively short amount of time.