As soon as 4 rolls around, I'm done with the money making portion of the day and the rest is just entirely fun stuff. I couldn't care less if what I'm doing isn't ever going to make money, it's just fun / interesting / satisfying curiosity.
I run - but I know I'm never going to make money running. I climb - but I know I'm never going to make money climbing. I code for fun on my side projects - same deal.
That work mindset gets turned off hard at 4pm.
I used to think less about people who check out at 5pm - how can you just leave and not give a shit that the code is a mess? - but as I grew older, I understood that they don't associate their self-worth with work. Their value system is different, and it's got benefits, like better mental health.
As someone who checks out at 5pm, I think you're looking at it from the wrong POV.
The main thing that drives me is the projects I work on in my spare time. I care that _that_ code is a mess. So, I might do a bit of work on that in the morning, but then start my actual paying job at e.g. 8am.
So how can I just leave my hobby project and not give a shit that the code is a mess? Because I get paid to do so, I have to work on whatever my boss wants me to work on because that's my job -- but as soon as 5pm hits I get to think about the stuff I really care about again.