Flying LAX to SYD and return in Delta Premium Select, at least 30 of the 40 seats wer empty, despite economy being full. I was curious about this, and learned that Delta had made a decision to largely stop bumping passengers up in many cases because they felt that they were passengers who would have paid for PS, but it had gotten to the point of passengers taking their chances ("I'll buy a Comfort Plus ticket, that usually gets me upgraded, and is cheaper.")
The flip side is that those upgrades were a cheap way for delta to buy loyalty. I know a lot of people who flew many times a year on delta only and now look for other airlines.