I’m surprised that anyone gets an upgrade. I’ve been Diamond for a couple years now and have yet to receive an upgrade. Not at home, not even abroad.
Out of curiosity and as a data point: Diamond via Credit Card, or Diamond via nights/stays? Many have reported a trend that Card Diamonds have fewer upgrades than night/stay/points Diamonds.
I for one am almost always upgraded in some way or another, Most of my says are NOT in the US, and I am unable to get a US Credit Card which gives status.