Well the environemnt greatly changes in a 24 hour period which would have had a large affect on the evolution of agents. Typically for a period of each day its dark and cold, not a very efficient time for an agent to operate on average. Perhaps its more effective to be productive during the time when they can see easily, and its warm so cold blooded agents can operate and then an ecosystme builds around these things etc and its no longer about jst the physical ebvironment but the ecological niche an agent is operating in. So no point being active at night if the flowers aren't awake, and the bugs that feed off the nectar aren't there, and thus your food isn't about.