Because there may be a couple of reasons why the ball didn't travel 5m.
- If a player in either of the 2 lines runs forward before the ball reaches the 5m line - it's a FK offence.
- If the thrower mucks it up - then there are options.
That can't be the answer because these are laws in relation to different aspects of Touch: The QTI and the line out.
World Rugby Law Book said:
Quick Throw
6. The ball must reach the five-metre line before it is played and a player must not prevent
the ball from travelling five metres.
Sanction: Free-kick.
We also have the following law relation to a QTI
4.
b. Parallel to or towards the thrower’s own goal line;
and
c. So that it reaches the five-metre line before it touches the ground or hits a player;
and
Sanction: Option of lineout or scrum.
6 seems to refer to the actions of "Other players" at a QTI where as 4 seems to refer to the thrower in.
Whereas:
World Rugby Law Book said:
Throwing into a line out
23. The ball must:
a. Be thrown in straight along the mark of touch; and
b. Reach the five-metre line before it hits the ground or is played.
Sanction: Option of lineout or scrum. If the lineout is chosen and the ball is again not thrown straight, a scrum is awarded to the team that originally threw in the ball.
Here the actions of both the thrower (a) and the "other players" (b) have the same sanction.
For both the ball must travel the required distance (thrower-in's issue) and must not be played before it reaches the required distance. (other players' issue).
So why treat a QTI and a full line out differently in repect of the actions of "other players"?
With a QTI the ball need not be straight (it can go backward as long as it crosses the 5m line). Why? Not material I hear some say. BUT surely the same would apply to QTI caught before it gets to the 5? No? Also rarely would a QTI be intercepted by the opposition before reaching the 5.
I like to ask the question "what is a law try to achieve?" it helps interprets it at times. That is not helping here.