The "no availability" is a big deal, so good luck with that.

I am also Plat, travel every week domestically and haven't received a complimentary upgrade in many months. Almost every place I stay says " we're fully booked for tomorrow" whether they are urban, suburban, rural, West Coast, East Coast, etc.

I check in on the app almost every time, give estimated arrival, chat or call the front desk, ask again upon checkin, all to no avail.