A proper metal sword will flex and bend out of shape when a wooden sword would crack and splinter into sharp edges, which can have horrible results if you are using it in a mock fight.
SCA uses rattan weapons (well, we also use steel weapons, but mostly in single combat) because a rattan stick will break in a clean way. It starts going to "mush" and when it breaks it looks like its been sawed in half, so no threat of piercing your friends eyeball if your sword breaks during a fight.
And I prefer safety in these kinds of things. If you want to see what happens when you minimize safety take a look at Russian steel combat or this:
http://en.wikipedia.org/wiki/Battle_of_the_Nations_%28Medieval_Tournament%29I'd rather be the pussy who does things safely. I mean I know people over 50 who can still do armoured combat or fencing because they haven't broken themselves. I totally understand why re-enactment combat using steel weapons rarely if ever has charges against shield walls, or stabbing. SCA does both of those with rattan weapons (The most fun I've had in SCA armoured combat has involved shield walls and charges, wether charging or being in the receiving end.) but that is a bit safer.
And since I mentioned BOTN I must include a video, here Team USA vs Team Poland from 2012:
For the record, the people chanting "USA! USA!" are from the Russian team since they thought it wasn't right that the US team was the only one without fans. (This was their first time and not many people came as a spectator from overseas.) Also for the record, although some of that is cool I will never ever try to enter that tournament or anything like it since those rules are insane.