Pyramid schemes are not self-sustaining. They rely on the continual gullibility of exponentially larger numbers of consumers. They fail when it becomes apparent that you can't fool all of the people all of the time.

But that doesn't keep a few shysters from playing the game. They win by getting out before it blows up. They know that you can fool all of the people some of the time.

Continuous recruiting. One gets two, two gets four, four gets eight and so on.
Potentially it is mathematically it is possible to make money if you are in at the beginning of the pyramid otherwise known as being on the ground floor.
Realistically, well do the math.

Unfortunately, most people are uneducated in what a pyramid scheme really is. All pyramids are illegal. Multilevel Marketing is not a pyramid scheme and is obviously totally legal or it would be shut down before it ever got started.
Multilevel marketing is just a different method of marketing a product than commercial. With a commercial business, eg your local grocery chain, they choose to market products in a store setting which ensures regular customers as well as convenience. Now the Manager and the guys at the top earn the best income, cashiers and stock people earn close to minimum. This is because they have a great deal of overhead, the store itself, employees, lights, advertising as well as logistics.
Multilevel companies market in a different way. They choose to not have a store or do advertising commercially, instead they have the people in the field do the selling and pay them to ensure the product gets into peoples homes. The people in the field essentially own their own business and one of the perks is tax write-offs, just like the commercial businesses have.
So you see it is just a different way of directing the dollar but still marketing just the same.
The reason MLM companies choose to do business that way is because they normally have a unique product that they don't want sitting on the shelves in a store. They want people to put the word out on what their experience is with the product and that is done by presenting it personally to people.
I have found great success doing this and part of my job is to ensure the people I bring into the business also experience success. As long as they are treating it like a true business and putting work into it, they cannot fail because their support team is there to help them every step of the way.