Because in this context, only murders are relevant.
For example, describe a set of gun laws, outside of widespread banning of all guns including handguns, that would significantly reduce gun death by suicide.
The assault weapon laws everybody's talking about now? As far as I'm aware, a large magazine or semi-automatic operation does not make that much difference when shooting yourself. Unless you are a really, really bad shot. A typical gun accident also usually involves one bad shot. A gun accident involving multiple trigger pulls is suspicious.