I believe it’s required by 210.12(C). Article 100 defines ‘guest room’ and ‘guest suite’, and includes the bathroom
N 210.12(C) Guest Rooms and Guest Suites. All 120-volt, single-phase, 15- and 20-ampere branch circuits supplying outlets and devices installed in guest rooms and guest suites of hotels and motels shall be protected by any of the means described in 210.12(A)(1) through (6).
Guest Room. An accommodation combining living, sleeping, sanitary, and storage facilities within a compartment.
Guest Suite. An accommodation with two or more contiguous rooms comprising a compartment, with or without doors between such rooms, that provides living, sleeping, sanitary, and storage facilities.