As was already mentioned, the nylon coating was intended to reduce airborne lead dust when used at indoor ranges.
Can I be the only one left around here who remembers the media feeding frenzy about "cop killer bullets"? The story line was that the nyclad bullets would penetrate police body armor, so this ammo was designed to kill cops and should be banned. A number of Congress-critters joined in the chorus.
That this product was developed specifically for police use, and the overwhelming majority of production was delivered directly to law enforcement agencies, did not stop the screaming media machine once they got started on their "cop killer bullets" mantra.