It started for me when I retired. Still lots to do, but no specific time to do it, so I enjoyed sleeping past 4:30 am. Later up meant later to sleep the next night. After about a year, it came down to sleeping 3 to 5 hours a couple of times a day whenever the mood hit. It is a really weird schedule, but I don't see it as a problem.
I just don't want to be up at this time of night. Earlier today, I had 4 people stop by all at different times, just to chat. I love having them come over but I wouldn't have time for a 3 hour nap. I can set my own hours because I work from home but then there's that also.
This is just the most convenient time to sleep, dang it!