The Consumerist article (and maybe the Bloomberg piece which, surprisingly, seems to date from February -- so maybe this has been happening for a while and nobody on FT yet noticed?) noted that AA benefits from offering snacks rather than vouchers because it keeps people in the gate area.

That's quite a clever move -- cheaper to pay to keep people nearby than pay IDB or compensation if they are offloaded if they don't come back to the gate when the plane reboards and departs.