In Worms you have a lot of time to think about the shot you are going to make. In Soldat you don't, and you wouldn't be able to nade* someone who is coming to you and kill him, because the grenade would just bounce and explode whenever it's away from any enemy (yeah i bet that would always happen).
Also, 5 (seconds I assume) would be a LOT, or at least enough to make sure the grenade is going to explode on the ground. Keep in mind that in Worms you can throw the grenade much further than in Soldat.
*nade
verb.
  To throw a grenade to someone or something.
noun.
  Grenade.