> Customers who really need that will go find it at Walmart, or where-ever.

So here's a weird externality. As a decently well off tech-worker, I don't care if I'm paying 5$ or 2$ for lightbulbs, even if I'm re-lighting my whole house. The seller will sell on Amazon, because it is the largest market and will set their prices on other markets to match Amazon. I'll buy on Amazon, because it isn't worth my time to check multiple websites to get the best price (especially when SKUs differ and I have multiple other items I'm buying, etc). And now people who do need to save money, can't also find this lightbulb at a cheaper price on competing marketplaces, even if this lightbulb is actually the best quality.