Of course it will never prevent the sledgehammer approach but it does go some way to prevent more subtle approaches.
BTID and password needed for the BTApp I presume. Not to access the router. (Admin password).
No mobile devices so BTApp details are irrelevant.
It appears BT have created a function on router a you cant access unless you buy an Apple or Android device. A big backhander was on offer no doubt.
Access control can now only be accessed using BTID and app password via a smart phone/tablet, router still needs admin password but access control is not available.
As previously stated, it is an attempt to make access control less easily circumvented. I guess you are the one household in the country that wants access control but doesn't have a smart phone.