What the hell happened to upgrades?

I’m a Diamond, and haven’t been upgraded the day of a flight in quite some time. After checking in yesterday I was 1 of 23 on the list with 2 available seats. This morning 2hours before my flight I was still 1/23 with 1 seat available. Before my flight it shows no available upgrades. Just curious who are getting these seats? This has happened on my last 3 trips this year. Thanks!