Another factor is that, for seats sold on the open market (ie not part of a package deal - think easy, FR etc) there is a customer cut off at about 1.30-2am local time. Arriving before that time, most pax view it as possible to go home and get a few hours sleep before getting up for work later that same day. After that, the pax are looking at an extra day off work.
For package deals (Tui etc) you are booking from X date - Y date, so whatever gets you the most time away in that window is what most pax are after - if a flight landing at 4am gets you an extra day in resort, they’d probably take it.
Why the package logic didn’t apply to people booking their flights separately, the Revenue Management people didn’t know, although they had their theories. But their numbers reflected it, time & again.