You don’t buy the product and store it, you just find the customer and the distributor mails it directly to the customers, not you.
In a pyramid scheme, you would be buying the product and holding onto it.
In a pyramid scheme you would be tricking others into buying junk for "their own businesses" to sell to other people.
Drop shipping is nothing like a pyramid scheme. It's just a form of arbitrage. You buy from one party for less money and sell to another party for more.