It's in the rules. A player who spends too much time on the ground (acting or otherwise) must be carried off, and stay off the field until the ref allows him back on. In theory, it gives a temporary advantage to the other team. In practice, it doesn't work.
FIFA requires that the stretcher be brought out so that the game can continue. The player either gets on the stretcher or gets up. It is intended to stop the delaying tactics.