Maybe this isn't a new situation, but it doesn't seem to be well covered here and it's certainly new to me. Details:

Bought a ticket in coach USA-Asia (B-class in this case, but not relevant to this story) and applied to waitlist a mileage upgrade. Now, when I booked I knew there was no upgrade space available, but I looked at availability and things looked pretty good. And yes, want business buy business. As far as I'm concerned full fare Y + upgrade miles = buying business but whatever.

Fast forward to 48 hours before departure - still no upgrade. C-cabin has 16 open seats (confirmed by calling) and Y-cabin still has 50+ seats. Fine.

Agent makes it very clear - do NOT check in at 24 hours as once you check in, mileage upgrades can't be processed. Wait until you get to the airport in the hopes it clears a few hours before departure. Fine.

Fast forward to 3 hours before departure - 16 open seats still in C, 50+ in coach. No upgrade. Well, I now need to check in and the airport says they can't process mileage upgrades. I ask if 16+ Diamonds using GPUs are on the upgrade list or will the cabin will leave empty. 0 on the upgrade list - cabin will leave empty.

So, I call in while standing at the airport check in line. And I fight - hard. Long story short they open up space because everyone agreed the situation was "absurd", but that it's hardly ever done and not to expect it in the future.

So what am I missing? This is a catch 22 - they won't open up upgrade space until the gate opens, but they won't transfer mileage upgrade requests to the gate. So essentially unless a mileage upgrade is available at booking, the program is 100% useless.

Any suggestions on what to do for my return in a few days, which looks to be trending the same way as my outbound with a fully open cabin but no upgrade space?