I could see the contrusction workers actually working, moving vans with families, kids boarding coming out of the house, boarding the school bus (actually walking/climbing), going to the school, playing on the swings, the sand, the slides, people actually walking in the park, a car actually owned by a sim being parked at work, etc. SC5 is praised for this level of detail in its model.
TL;DR: There were a lot of decisions SimCity made that directly increased the number of agents required. This in turn directly impacted the #1 issue about the game: City size.
It's similar for other games of the time, like Settlers II. Only in the 2000s the detail level was massively cut down.
SC5 might have been really pretty, but the agent simulation was entry level CS at best. As others have noted, sims woke up and drove to the closest available job regardless of past behavior for example.