Springfield "comes to life" only sometimes

Some times many buildings and items in my Springfield will "come to life" or become active without having a character do a job in them. Krusty's giant wheel has kids riding them (otherwise it sits empty), chinese restaurant has lights on and people inside (otherwise its "off"), tavern on the scream's mouse chops off entrance (otherwise inactive) and others that i cant really remember. Anyone knows what triggers this? Like i said no character jobs were being done in any of the buildings. Thanks!