An autosave feature would have to be optional, and I recommend toggled "off" by default.
Lots of simmers (as others have commented) quit without saving when something bad happens that they don't want for their story.
I also quit without saving on purpose when I am shooting screenshots for my very scripted simit story. The day goes too fast in this game and the lighting changes too quickly. To get all the screenshots I need for the story, I set everything up at the start of the time of day that I want, shoot as many screenshots as I can until the light changes too noticeably, and then quit without saving so I can come back into the game at the starting point of that lighting and shoot more screenshots I need to finish the scene.
An autosave feature that I can't turn off would make this impossible.