If which metalcore only uses clean vocals?

metalcore is the most astounding genre..i was fascinated by their emphasis on melody,which was not executd by any metal or rock genre before...but the problem is that they only use unclean vocals (such as Parkwaydrive) or fuse a little clean vocals in the song....people despise such songs due to distorted vocals,they dont pay attention to the freaking melodic lines...so i suppose that if metalcore artists only use clean vocals,there is a big probabilty that it will be the mainstream genre...some bands are starting to concentrate more on clean vocals(bullet for my valentine)...it will be more important than rock and that clic metal crap(metallica) which most people adore....so why these artists dont only use clean vocals?(unless you like screaming)