About Basic Strategy

I am new in blackjack and I have a question about the basic strategy of "6 Decks, H17, DA2, DAS, OBO, No surrender", hoping that someone can help me.....
the chart says that "for A,6 : Double vs 3~6,o/w hit"....I am wondering why o/w hit instead of o/w stand since we should always stand on 17.
This maybe a dumb question for you guys,but it will help me to learn quickly since I don't quite get it...thanks