I can't speak for others here and we don't have SATs in this country, but these things can be very unfair. When I was seventeen, I had a lot of things to deal with which were not of my own making, such as caring for a terminally ill relative and wondering if I would even have a roof over my head a few months down the line. That kind of thing tends to take your mind off school work. Several years later and I was in a much better place.

I think it's fair enough to say teenagers in general have more instability in their life even without this.

If you think it matters (I don’t) and think you scored unfairly low at 17, you can take (or retake) the SAT at any age.