It's very simple: since already invested 12BB, it is profitable to call due to pot odds with certain hands. So, AJo hand is not included in the list of these hands, because heavily dominated: if a jack comes, you will lose with top pair with top kicker to hands AA/KK/QQ/JJ, and if an ace comes, you will lose with top pair to hands AK and maybe sometimes to AQs.
And if you call with A5s, then there is a chance to win if a good board comes, and if an ace comes and your opponent bets actively, then you will just fold and not lose too much.