I could see leaving them home alone for a couple of hours, even a few hours once in a while.
But what you are describing is a recipe for disaster. Even though there are families that have done it, and get away with it, it usually done so with negative consequences. If something tragic were to happen, the parents can hardly blame a 12 year old girl for not being mature enough to handle emergencies.
On a personal note, I used to work with a woman, whose parents did this to her and her brother, gender and age reversed. And her brother coerced her into sex for several summers running. Then he started bringing his friends over for some action and that's when it finally ended.
I would venture to say, she's still in therapy to this day, or still going from failed relationship to another. It was WAY too much alone time for just 2 kids.
I feel sorry for those kids that the parents believe they'll be OK for so long. Super irresponsible and lack of judgement IMHO.
And on another note, I'm from a big family, and we were left home for a week or 2 alone at times during the summer, with my sister and I watching and caring for the 4 younger siblings. I hated it. I resented the amount of work it was, constantly diapering and feeding babies, toddler and younger kids. Clearly a different age spread and my parents were borderline stupid I think. Even with all that work and responsibility to keep us busy, there were predators in the neighborhood that knew our parents were out and about for extended periods of time.
I vote it's a HUGE risk nowadays.