Just because the rules of cricket aren’t written into the very fabric of the universe doesn’t mean there are no rules by which we ought to play, should we choose to do so. And just because we’re not rationally obligated to adhere to this particular rule set, nor bound to follow these rules on pain of eternal torment from some otherworldly being, will we simply start playing by any rules we choose.
And yes, if everyone resolved that cricket was not much fun and decided to abandon it, or concluded the rules should be changed to resemble badminton, then cricket, as a sport, would necessarily change.
But, given the serious import we all place on morality – as well as the benefit it lends us all to play by its rules – it’s even less likely we’ll ever, as a group, decide no longer to play, or decide to change the rules so that it no longer resembles morality.
Morality, like cricket, need not be necessary in order for it to be important enough to concern ourselves over the maintenance and enforcement of the rules.