Because they are just a bit too ricerish for my likeing, why I'm opposed to having lights in the skin files
Personally I don't like seeing pretty patterns in my lights, others do, those aren't that bad, there nicely done but not a style I'd go for, putting lights in a skin file would just add the potential for badly done MS Paint jobs, nothing worse than low quality .jpgs save in MS Paint racing round the track that look like they've been covered in pixelated bird shit.