Hey, new user here.
Just had to wonder why Sims don't bother repairing broken things? I left the Sims running for probably 10 minutes and the only toilet in the house broke and everyone peed their pants. Wouldn't you fix your toilet before peeing your pants?
Most people in real life have no idea how to fix a toilet the Sims are no different. You can build up their handiness in which case they may start fixing broken things by themselves.
As jpkarlsen said, sims need to sufficiently develop their handiness skill to fix things. They cannot do it as they please. Even so, they still don’t often fix things on their own. You typically have to manually select/direct your sims to fix an object, no matter the skill level.
At maxed skill for handiness - auto repair in your own household should be a given
