The same reason someone would listen to any other genre of music. It sounds good.
I would recommend Dark Tranquility's new album fiction to any metal fan. Its amazing
Metalcore/hardcore has its place. But it gets a bit repetitive after a while. In my opinion anyway
My favs are:
Machine head
Dark Tranquility
Draconian
Immortal
Bolt Thrower
Killswitch Engage
Mnemic
DevilDriver
As i Lay Dying
In Flames
Dimmu Borgir
Cellenish Circle