Because it’s a weird afterthought. You roll huge bunches of dice to hit, in a very unsubtle fashion (there are no modifiers for range, so it’s essentially your shooting rating plus whatever is needed to add up to 7. There’s a table to disguise that part) Then, because that’s far too many, you roll a ‘to wound’ roll of all your hits, which basically halves them. Then the target player finally comes back from taking a smoke break while you did this, and rolls that number of dice to save, according to his notional armour strength.
As a mechanism it’s unnecessarily slow, clunky, barely interactive, and still ignores a lot of the modifiers that most of us think of as standard.
I do all my own stunts.