Tepi62Ka: You have better ball in bag [...]
This is not quite correct.
One ball type is in your bag while the others are in your inventory - think of your garage, equally inaccessible during a round.
The major reason is, IMHO, that the bag is closed during a game, following the official Rules of Golf which forbid an exchange of clubs. Here, the balls are "collateral damage" of this fact (and early programming). They only forsaw the Starter as a common replacement.