That's my thing too -- I very much enjoy going out evenings & nights, often fairly late, most weekdays. Getting up reliably before 9am when I'm out until 12-2am (perhaps followed by working for a couple hours, or just winding down), is difficult enough to be not worth trying for me. I'm single right now, but when I'm with someone who goes to bed much earlier, I suppose I do sometimes shift my schedule earlier as well. (I guess that's similar to one of the OP's justifications of doing this to have more time with his wife.)