If AJ went for the KO, he'd be opening himself up un-necessarily. Instead, he went for the simple, safe option with his reach and jab.
https://www.stuff.co.nz/sport/combat-sports/103198917/anthony-joshua-explains-why-he-couldnt-knock-out-joseph-parker-in-their-heavyweight-unification-fight
https://www.stuff.co.nz/sport/combat-sports/103198917/anthony-joshua-explains-why-he-couldnt-knock-out-joseph-parker-in-their-heavyweight-unification-fight