It's just a pure numbers play. Most people won't be interested at all. They booked their flight on Saturday for a reason.
But if AA emails all 150 people on your flight and even if only 2 or 3 people take the offer, then that's 2 or 3 people less that AA will have to rebook if they're expecting irrops, or offer compensation to if they're expecting it to be oversold, etc.