When I was VP of Engineering org for a startup, it was a group of about 30 Engineers at all stages of life. Some were young w/no obligations, some had families, a couple were single parents, and there were even a couple folks in the starting to have grandkids phase. I didn't particularly care what schedules people kept as long as work got done and they could be predictably reached.

As a result, there were people that worked 6am to 3pm(ish), 10-3, followed by 7-10 in the evening, 11-8, etc. I had a young child and handled school dropoff, so my hours were roughly 9am - 6pm. My boss, the CEO, was a workaholic who arrived around 10am and worked to whenever. I spent an amazing amount of time dealing with "where is everyone?" sorts of questions, despite the team running fairly efficiently and still completing work on aggressive schedules.

The issue is that there are very few jobs where you can basically ignore the rest of the world (or even the rest of the world in nearby timezones). If you're a solo writer or programmer sure. But if you work with other people, not wanting to have meetings before 2pm is often a problem. (As would someone who wanted to work midnight to 8am.)

Even jobs that are quite flexible are going to want some overlap time and, even if an atypical schedule allows for a few hours of overlap, the reality is that people will get tired of always having to schedule around your preferences.