It's a gentleman's game. Like in golf, there are expectations of behavior.

They didn't think they needed a rule.

This was what made me certain they were wrong--the commentary of their own older brother, who's hugely respected:

> As the ball was being bowled, Ian Chappell (elder brother of Greg and Trevor, and a former Australian captain), who was commentating on the match, was heard to call out "No, Greg, no, you can't do that"[10] in an instinctive reaction to the incident, and he remained critical in a later newspaper article on the incident.[11]

The problem here is that limited overs cricket has been modified from regular test cricket in a way that fundamentally alters the strategy and flow of the game to increase the action and decrease how long it takes to play.

Because of those concessions to speed and entertainment, some rules that worked ok in test cricket break the game in limited overs. In this case, NZ was down to their “final over”, a concept that doesn’t exist in test cricket. Underarm bowling basically removes overs from the game and can guarantee a win for the bowlers, but in test cricket, would lead to a draw.

It's pretty much completely not like playing the game, because the batting team can't meaningfully hit the ball.

In context, it was a bit like taking advantage of a videogame exploit that others variously hadn't discovered, thought was forbidden, or assumed would not be used by tacit agreement.

> Cricket will never make sense to me

Cricket is my analogy for life: a lot of standing around, interspersed by bouts of running back & forth often with people shouting at you, and a scoring system that seems almost as deliberately obtuse as Mornington Crescent (the true gentleman's game!).