That's because every Nu-Metal band directly ripped off one of these three bands.
1. Souls at Zero (shoot, their drummer is even IN Godsmack)
2. Mordred (first metal band to have a DJ)
3. Prong (Riggs, from Rob Zombie's band literally uses exactly the same setup as Tommy Victor did on Prong's Rude Awakening and he's not ashamed to admit it).
Prong started as a hardcore punk band, morphed into a thrash band and then morphed again into an industrial metal band. They were way ahead of the curve with their last two albums. Check this out - the last Prong studio album (not counting the new, Scorpio Rising) was in 1996.
Anyway...
Ozzy - Bark at the Moon, Ultimate Sin
Maiden - Wasted Years
Metallica - Mastertarium
Slayer - South of Heaven, Spill the Blood, War Ensamble
Sabbath - Iron Man, N.I.B
Prong - Beg to Differ, Who's Fist is This Anyway, Rude Awakening