Why do rugby players slide to stop?

Answer 1

if you are talking about when they score a try then (in both codes) diving firstly makes the ball carrier harder to stop as their momentum drives then forward, secondly lowering their centre of gravity again makes then difficult to stop and now with more complex defense s the defensive players will frequently try to place their body between the ball carrier and the ground which then makes "grounding" the ball more difficult and can force the ball carrier to make more than the maximum 2 movements to the try area which if they do exceed 2 movements they will be penalised for this.

The rules are clear in Rugby the ball must be placed down in a controlled manner.