Getting up in the dark reminds me too much of the Army. Also it would annoy my woman.
I'm self-employed, so I can set my own hours - in principle I could train any time. In practice, mid-morning I'm busy, in the evenings I want to be with my woman or friends. Put in the meals and an hour or so's digestion time, and that gives me mid-afternoon, 1500-1600, something like that.
Also, my gym is most crowded 0700-0830 and 1600-2000. I don't like it completely empty, but I don't want to have to wait for every exercise.
Mind you, those peak times are only really Mon-Wed, later in the week it's quieter, and even - surprisingly - on the weekends. Perhaps I should change my workout days...