People who don't know any better get sold on the "be your own boss, earn what you put in" concept. Reality doesn't match expectations. The people work their asses off and wind up with a lot less money than they expected because costs and actual spent time aren't taken into account. The people they're working for continue to make lots of money. People quit, but are soon replaced by the next sucker.
MLMs still exist and are going strong, but culturally we're more aware of what they are. But maybe we're becoming more aware of what "gigs" are.
Perhaps, and I both love and hate myself for saying this, 'the gig is up'?