the pitcher must also stay in the pitchers box/ vicinity of the rubber, for the duration of the at bat as to not form their own type of step out while the batter is glued to the box. fair is fair neither batter or pitcher can delay the AB.
one continuous at bat. if the batter knows that he won't be given time to step out and gripe a strike call you also reduce player to umpires interactions because they will have to focus to the next pitch coming.
absolutely nothing is dumber than stepping out 3-1, watch a perfect BP tumbler and need to step out again before the full count pitch.