If that were standard policy then parents might get the idea to let their kids just spend whatever they want on FB games knowing it'll just get refunded, effectively scamming app developers.
The burden of checking age for each transaction should be with the seller, as it is enforced in retail. If the seller doesnt check for proof, then the transaction should be trivially refundable at least.
This software exists solely to manipulate irrational gambling tendencies.
And even putting the kid issue aside, anything that discourages repeated-purchase IAPs is itself a net benefit to gaming and app development.