As a founder you would probably spend more time on calls and other administrative tasks that don’t require much brain energy. That’s how you end up doing long hours.
I guess each person has a different time of best performance, the problem is when you get a job in a office without flexible hours.
Edit: grammar
Since I've forced myself to go to sleep no later than 11, I've realized that hey, I actually am a morning person.
However despite a few years of this routine I still find myself more productive at night than I am in the morning (or even during the day, unfortunately).