Fair points - I would prefer a paper coffee cup over the plastic cups any day. I hate the plastic cups. As for why, COVID safety holdovers. I usually only use glassware at five-star properties anyway because I have the (likely mistaken) assumption that they have been cleaned more effectively.

From what I can remember, most standard Marriotts got rid of glassware during COVID and since. They had the wrapped plastic cups, which you could also steal from the fitness center.