It is animated in 3 directions because there are 3 uniquely made animations.
For left / right a simple mirorring does the trick and that's how most topdown games handle it.
If I'd say 4 directions this would mean that the sword would need to be uniquely animated for the 4th direction, which is not the case for this template. The sword will flip the hand - again that's how it is handled in most games.