@matthew_d_green >Why won’t Apple add a disappearing messages feature?
That is because they want to be able to command their devices to decrypt and send them whatever messages they want via the backdoor in the future, with little chance of them being deleted (after all, they don't get deleted unless both ends delete them, even though the deletion function may not actually delete, just like how apple has accidentally restored years old "deleted" images from "icloud").

If you don't have the freedom to change the software in freedom, you will not be able to get wanted features unless the master feels like adding them.