Why do people think that one genre or sub genre of hip hop/rap can kill off hip hop?

On one side mumble rap is bad. I can't stand it myself but when it comes rappers singing I don't mind it at all. I don't always like it or love it but it is what it is. I think when rappers pull it of well such as Kendrick has done it can be great. I think Asap Rocky can also pull it off well too.

Aside from that there's always dope underground and indie artists out there if you don't want to hear mainstream stuff. I also like some mainstream and semi mainstream hip hop. While I feel that hip hop is on somewhat of a decline don't feel that it will die off anytime soon because of mumble rap.