According to the argument given by the earlier replies, a good MLM company offers products in return for the money spent on the registration. Automatically, your money is returned in terms of products just like buying an item in the store. Your money = products with the same valuation as the money spent. So basically people do not lose at all. While money in gambling, when lost won't come back.
I don't consider an MLM as a good company. Products are too overpriced but that's what you get with your money instead of having no return from your purchase.
And aside from products, whatever incentive the MLM company gives will make them attract their customers to purchase those and not just the products alone.