See, it's confusing. It would make more sense if they could reduce it to a percentage between 0 and 100, I think. It'll probably never change, but that doesn't stop it from being silly.
It's not that silly. When you receive your SAT score you receive a grade out of 800 for each section you write (this is the way it used to be at least), and
you also receive the percentile you place in on each section. Your score out of 800 is primarily determined by your percentile score, and so the college board scores are less confusing than a raw or scaled percentage grade.
You then might think it would be more clear to just give a grade out of 100 that represents the percentile grade, but that isn't really the case. From test to test there will be a slight variation in the types of questions, difficulty of questions, and quality of students taking the test, and so this is all taken into account as well when assigning the grade out of 800. So avoiding numbers like "100" dodges the confusion that would arise out of interpreting the SAT score as solely a percentage or percentile grade.
The system makes perfect sense and it's well thought out.