There are a lot of purists in the metal genre, and a lot of those folks are of the white male demographic (with the possible exception of funk metal) who are usually resistant to change their sound lest they be considered a sellout. (Hell, Metallica and Megadeth got flak for changing up their sound) Also, the criticism is largely seems to more focused in the West (particularly in the US and Western Europe) than in say Japan or South Korea, where it is usually much more accepted, or at least judged not as harshly. About the only nu-metal band that most purists don't go after is Slipknot, (and they don't deny their nu-metal roots even when they gotten away from it) Deftones and maybe Godsmack. (who were able to shift their sound without being trend hoppers)
Now, I will point out that there are also defenders of nu-metal, metalcore and other sub genres of metal within the community as well, who at least acknowledge that these off-shoots aren't really that bad, albeit mostly because hard rock that isn't over 30 years old is losing radio play with a few exceptions, not that they necessarily needed radio play before. In fact, I made a similar point about this in an earlier post about nu-metal became a scapegoat genre in the mid-2000's due to its overexposure.
Simply stated, the purists (both from fans and even certain bands) shunned many metal offshoots in the west due to a mix of close-minded thinking, disdain for other genres and the fact that said metal offshoots got more appeal to different demographics that weren't their own. This has died down somewhat during this decade (as with hair metal in the 00's) due to modern hard rock being marginalized by the mainstream and nostalgic reimaging of their youth, for better or worse.
