The PM has had this wording about this room for years. They should be applauded for offering this particular room at a very discounted price, rather than trying to pawn it off on some unsuspecting guest. They are very, very upfront about this room and this policy. If you are willing to take this room, you know ahead of times there will be no UG.
The T&Cs are clear that UGs are at the hotel's discretion.
Complimentary Room Upgrade: Based on room availability at check-in and limited to a Member's personal guestroom. Upgrades may include rooms with desirable views, rooms on high floors, corner rooms, rooms with special amenities, rooms on Executive Floors, or suites. All upgrades are granted on a space-available basis, as determined at the time of check-in. Upgrades are subject to availability and identified by each hotel. Not available at Marriott Vacation Club.
In this instance, the hotel has identified that UGs will not be available if you book this room type. The hotel could wait until the time of check-in to let guests know, but is very upfront in letting guests know both before booking and after booking.