Like biological parasites, the long lasting ones seem to have optimized the level of damage and chaos they cause, along with maintaining protection mechanisms (lobbying, political donations, corruption) that enable them to continue to survive and be incredibly lucrative to their founders.
It doesn't stop people joining, unfortunately. Knowing that Sue, the really successful seeming Super Global Ambassador Tier leader at the presentation on Saturday earned less than a shelf stacker does not stop some people figuring if only they join Amway they'd be doing better.
In Ponzis and Illegal MLMs, there's either no product or a sham product to disguise money from new recruits paying off the lineage.
Legal MLMs are legal because there's a more legitimate product that accounts for a larger share of revenue.
But even for-profit corporations that need to grow to survive share some features with the illegal variety, it's just that the real value of their products is a larger portion of their total revenue.