Why is Amway not sold in stores?

I'm curious to know, why is it that Amway products are not available for purchase in traditional retail stores? It seems like a popular and established brand, so what's the reason behind this unique distribution model? Is there a strategic advantage to selling exclusively through direct sales and independent distributors, or are there other factors at play here? I'd love to hear your thoughts on this intriguing aspect of Amway's business model.