I don't think this is strictly seen true: When you book let's say on the Edelweiss website, you only choose between Economy or Business in the first step (and other booking channels such as swiss.com doesn't even offer eco max which makes me believe this is just governed through the seat assignment).
Only later in the booking process on the EDW website, you have the option (but you are obviously not forced to) reserve a seat: Normal seat is e.g. CHF 29, Max seat is around CHF 200 depending on destination. Acknowledged that the max seat comes with small service enhancements beyond the seat. How does expertflyer represent Max?
Now what happens if a lot of people choose not to reserve a seat at all. Example: 20 passengers don't bother paying for seat reservation and there are 15 seats in Eco unallocated and 5 in Max.
If EDW doesn't release Max at check-in, they would have to stop selling Eco tickets when [passenger w/o set reservation] = [unassigned seats in Eco]. Would you then be forced after choosing Eco to buy a seat assignment? This seems odd as other booking channels, such as swiss.com would not allow you to pay for a seat assignment.
I will check what the load factor a day prior to departure and maybe I will be able to answer my own questions.