Because it's one on one, and because the dealer isn't forced either by house rules to go to 17+ and there's only one player sitting at the table the dealer get a wide bust out advantage because holding on 14,15.16,17 & even 18 statistically isn't safe.
Especially if the dealer is showing an 8,9,10,11.
Some one else at a real table especially if there's several people sitting at it could easily be holding 18,19,20 forcing the dealer to go for broke while you could just hold on single digits.
Essentially if you're at or below 11 always hit because you have about a 20% chance at landing on 18- blackjack especially if you have 11.
Ace's do roll back from 11 to one so if you have a couple low cards but an ace or two keep hitting because they'll roll back and it gives you a greater chance of stangin on 19-BJ