Interestingly, I recently got travel credit offers on 2 different flights. Neither of the 2 fligjts were sold out. Seats were available on both flights.

Then I noticed I had a different 3rd flight coming up in 3 weeks that was 100% sold out. No seats available for purchase. None. Zero. I felt certain I would get a travel credit offer for the 100% sold out flight. Nope, I never did. i flew that flight a couple of days ago at it was 100% full. Not 1 empty seat. Go figure.