I think that all of us have had the same experience at some point or another.

I sometimes push for an upgrade and sometimes just forget about it depending on the staff and the reason for the stay. I have had the "we are full" excuse once before when seeing availability online, and basically been told to leave them alone.

In any case I make sure that I provide feedback to the hotel/accor via the survey request after a stay and point out if they have been good or bad regarding the platinum benefits (and sometimes receive feedback from the hotel directly). I would like to believe that the good and bad feedback is used somehow to improve customer experience...