The US Department of Transportation requires US airlines to offer either the ability to hold a reservation for 24 hours without ticketing, or to allow full refunds on non-refundable tickets for 24 hours after purchase, for travel booked at least 7 days in advance.
For years and long before this DOT requirement American has allowed consumers to place reservations on hold. It’s not something they were forced to do. Effective April 1, however, American will be conforming to the rest of the industry. They will no longer free 24 hour holds and instead will offer only 24 hour cancellation.