It looks like some pretty heavy optimizations are needed if you want to be successful in one of those environments (daytime vs nighttime). Visual perception has to be fine-tuned for one of those environments. Perhaps thermal regulation is different too.

So I guess one possible explanation is that too many fine-tunings are required to work well in one environment, to allow the organism to be a good performer in both. So the logical choice is to withdraw from the other environment - just don't participate.

The parent comment only mentioned humans being diurnal, not other animals.

There's a number of strong evolutionary forces that explain nocturnality: niche differentiation, crypsis, a predation arms-race, water conservation, etc.

https://en.wikipedia.org/wiki/Nocturnality#Survival_adaptati...

I'm not sure your point about humans vs other animals.

Are you suggesting sleep evolved for a different reason in humans than it did for our ancestors and the millions of other species that sleep?