Apologies for the late reply.
A player "juggled the ball" and it travelled forward over the head of a potential atackler. The "ball carrier" ran round him and regathered.
Why didn't the defender tackle the attacker during the regathering? Was it because
a) the defender wasn't allowed by the rules?
b) the defender was slow to react/surprised/etc?
To be honest, i am not really concerned about b) and i don't see any evidence to support a). Let's call it an auto pass (that's what we called it in touch rugby back in the 80s), at it's extreme. You try that and you might get away with it the first time vs a much, much less skilled opponent. With a LOT of luck. The skill required is huge.
The other 99 times you will be dropped as you are a) liable to being tackled and b) you have your eyes on the ball (up) and not on your defender.
The regathering works if there is no defender close by. If there is, chances are it's better to drop the ball and give away a knock on than try to regather, give your opponent a free shot at your ribcage and still end up giving up the opposition a scrum.
chip to winger just inside touch, ball juggling tap begins, steps around incoming defender and goes into touch, loops round and back into the field of play to recover.
The obvious question then becomes: why is the defender in your scenario waiting for the attacker to regather in order to tackle him when he is allowed to do so
during the regathering?
Let me use your example, but including the defender's reaction
Attacker 1: chip to winger just inside touch
Attacker 2: ball juggling begins, steps around incoming defender
Defender 1: tackles Attacker 2 while the attacker's eyes are on the ball and his arms up trying to regather the ball, leaving his entire ribcage exposed.
rephrase: if something like this gets pulled off, i don't think it is because there is an exploit in the rules that gives the attacker an advantage. It is because the defender is not using his own advantage (focus, speed, exposure to being tackled, etc) to stop it.