So, I know a little about this, unfortunately. My "shameful past job" at one point in the 90s was working for a company that basically made small-business CRM+accounting software you could customize to drive any MLM scheme you could think up.
Amway's not the best example, since they actually sell real goods and because Amway's sellers' best customers have almost always been the sellers themselves. In other words, many sellers used it as a way to buy goods at "wholesale" and never really had any intention of reselling them. At one point, I think that was even part of the Amway pitch, particularly at the time they were inexplicably popular for their (expensive and therefore in theory a better deal discounted) water treatment products.
I don't think there's a price advantage there compared to Costco or online, though--much of what made Amway fade into the background starting in the mid 90s.
So too Stella Dot, Mary Kay, Cutco/Vector, probably Herbalife and even Transamerica, etc. They sell real stuff, whether or not the pricing makes sense, and you can technically turn a profit on it, whether or not the market is really there, so they're not technically considered a pyramid scheme in the scam/illegal sense.
Now, I'm not saying they're good ideas--at all--and they absolutely operate on hype and pipe dream every bit as much as those awful timeshare presentations. They have the same exponential market saturation issue as any pyramid scheme and the same diminishing returns--but they are generally not considered fraudulent, just obnoxious.
The really awful pyramid schemes mostly just sell "new seller kits" to prospective targets that teach them how to sell "new seller kits" to their targets, have no real product or way to make a profit, and the entire rollup is those kits and other overhead fees. They're the financial equivalent of a chain letter.
I'm pretty sure those do get action taken against them if they're identified. The biggest problem there is most are pretty small, take a bunch of people's money, then burn out once it's all rolled to the top ranks who founded the scheme and new marks aren't easy to find.