didn't have them before we saw the 3 km rule.
See the races pre 2005 when the 3 km rule came in. Any sprint lead outs were mainly done in the final km. Much less risk of a wreck going in the red for 30-60 seconds vs 3 minutes
This is a perfect illustration of the distinction between correlation and causation.
Sprinters tactics have nothing to do with the 3km rule because sprinters don’t care about time. The train tactic evolved to help win sprints and it becomes more or less prominent as sprint tactics evolve.