Being at home is the least safest place to leave a child 
More accidents happen in the home than anywhere else and a child left alone with the cooker/fire/candles/people knocking and calling at the door/people phoning/things in the house going wrong like floods or electrical fires is going to be in greater danger than in a park or playing out with their friends.
If you couple that with the mixed messages we give children at home 'don't answer the door/phone' versus 'how to get another adult to help when things go wrong' - no wonder we leave them at home later and later.
It takes a particular skill set and maturity to be left at home. You need to know for sure that they won't try and cook 'to be helpful', that they know how to open the door and which adults to get help from, how to deal with emergencies etc.
I left a 14 year old once for an hour and I thought I'd covered everything - I didn't cover the Gas board knocking on the door and being very forthright at getting people to turn their electricity off - the 14 year old didn't know where the fuse box was and was unnerved by the big blokes pushing the furniture out the way to get to it.
Anything can happen at home.
Obviously that same 14 year old had been going off by themselves for years and for hours perfectly safely with only himself to think about.
If you're in a house you feel responsible for what's going on in the house.