Moroseland It's what the reader base/market decides and they go with what's considered to be better for readers and writers. There will be very few novels that would not follow the predetermined concepts of genres that have already been established, so they don't bother with expanding it from their side.
And yes, no one will be hurt if they do add it, but as I said before, they go with why bother doing something that won't have much affect on them anyways.