re: Why don't they execute the read-option in rugby?

In rugby, you don't have an O-line, since blocking is illegal. So everything is in clear sight of the defenders in front of you. Also, the D tends to form a line across the field, so a forward handoff is not likely to get a defender out of position. There are offensive moves that are designed to trick the D, but they mostly involve the next man running laterally behind the ball carrier.