Based on my research, the DOT requires airlines to offer either:
1. 24-hour hold.
or
2. Refunds within 24 hours.
The DOT doesn’t require airlines to offer both.
Since AA offers 1, it doesn’t have to offer 2, so any lack of a refund for 2 would be governed by AA rules, not the DOT’s requirement.
I welcome all corrections if I’m wrong.