"I am 23 (started working in programming at 22) and this view confuses me. I don't want to sound rude but... you didn't have hobbies? Friends? Partner? Errands to run? Non-work programming projects? Even when I was single and lived alone, I had plenty of reasons to leave after 8 hours."
When I was 23 I had a very active fun social life as you appear to have as well. BTW I had the same opinions as you at that age as well.
The difference is most of those activities are at your discretion and OPTIONAL and you have enormous amount of 'myself' time available . When you have kids and a family your OPTIONAL activities diminish and your 'myself' time is non existent, due to REQUIRED commitments.
In addition staying up to 3am or 4am or all night sometimes was common for me at that age.
After having a kid and family you can still do that. The issue is your kid doesn't give a F that you stayed up till 3am to fix something and you have to take care off all your REQUIRED responsibilities throughout the day. After a while it takes it toll on you.