I read recently that risk for covid exposure on planes is highest when everyone takes off their masks to eat at the same time. Business and first-class seating were mentioned to be less risky, just because there is more space per person and fewer seats. So, maybe those who are flying are desiring to take less risk and opting for the "safer" seats (either thru $s or points). Or, as someone else said, just doing it nicer since there have been some missed trips. And, those who went into the pandemic with lots of money, for the most part, still have lots of money.....so what might be a splurge for most households, is no big deal for the truly wealthy (who may also be less tied to limited sick leave, docked pay issues, and medical evacuation issues, should a problem emerge).
Today (as the pandemic stands) I would NOT fly basic or preferred economy. And, if I HAD to travel, I would think long and hard even about business and first.....but I am admittedly being super cautious (for family risk reasons).
Using the same rationale as above (meal time risk), if 75% of economy truly remains unsold, that section may be where there actually winds up being less risk on that particular flight.......heck, you could have a seat with two empty rows in front and behind you :) Lots of social distancing :) and A LOT less worry about masks off during meal time.
Let us know how your flight shakes out and your thoughts afterward.