The bonus point is a bad trade and raiders keep taking it

One point for stretching across a line, against the risk of being caught by a defence that wants you to reach.

A raider crosses the bonus line, gets his trailing leg off the ground, collects one point and turns to run. It looks like free money. It is not free money, and a large number of raids are lost in exactly that half second between the reach and the retreat.

The bonus is available only with six or seven defenders on the mat. That is precisely the situation where the defence is strongest and where the raider's escape corridor is narrowest. So the rule offers its reward at the moment of maximum danger, which is either elegant design or a trap, depending on how charitable you are feeling. To claim it you have to overextend, and overextension is the single condition every ankle hold specialist in the sport is trained to wait for.

Do the arithmetic honestly. The bonus is one point. Being caught is one point to them plus your body off the mat, which weakens your next defensive set and moves you closer to an all out. The all out is worth two more. So a failed bonus attempt against a strong seven can cost four points of swing across a couple of minutes, and the upside was one.

I would go further. Chasing bonus is a symptom, not a strategy. Sides do it when they do not trust their raider to score a touch, and they do it most in the second half when legs are gone and someone on the bench wants activity on the scoreboard. The teams who win titles tend to treat bonus as something you take when the defence has already committed forward and the line is genuinely undefended, not as a plan you announce before the raid.

There is a version of the argument on the other side and it is fair. Bonus points break deadlocks, they keep the raider going deep instead of loitering near midline, and a raid that produces nothing at all is worse than a cheap one. Fine. But look at where the corners position themselves against a known bonus hunter. They shade in. They give you the line. They want you to take it.

When the defence is helping you make a decision, the decision is usually theirs.