AS has a “Change your flight for tens of dollars” program to try and shuffle people off overbooked flights before they get to the airport.

https://www.flyertalk.com/forum/alas...el-credit.html

They might luck out and find someone who booked a flight they didn’t really want, but the preferred flight was more expensive at booking time. Or someone’s schedule has changed, but they were reluctant to change due to fare difference concerns