Given that I need to get up at 5 in order to get to the gym at 6:30 (too much timewasting in the morning) so that I am at work at 9, everything after 21 is too late.
It's called being a parent. The kids must sleep at 20:00 anyway and at that point there is not much reason to stay to up much longer. A bit of putting things into order, a drink with wife, a quick chat then sleep.
Add personaltity change. This is completely anecdotal but I do hear stories about personality changes. More mellow, sure, but also less motivated and less likely to accept responsibility.