Marketplaces are about balancing out competing sources of stuff by roughly their quality value without oversight, provided the underlying 'rules' aren't too egregiously ignored (no committing actual crimes, no stealing things to sell them at prices below their worth, no lying or pressuring people to lie on your behalf or stealing their identities to lie with).
When you enforce a lack of crimes, marketplaces work to allocate resources without top-down control, and scale as big as you like without losing that quality. THAT is the point. It has nothing to do with discovery and in fact they're not at all great for discovery.
The person who allocates more money and energy to being discovered by you is always going to come out ahead of the one who worked to deliver you a better product and didn't put as many resources into, quite literally, marketing. All expenditures in marketing are literally you paying to be sold on a thing, literally you paying to distort the marketplace in the product's favor (regardless of its value, could be garbage or a Veblen good that is otherwise of unimpeachable quality)
The LAST thing you want is a marketplace for discovery. You want discovery to do an end run around the market and give you the realities of what's being sold. The market then allocates resources based on your hopefully enlightened input.
Other products can also be bought that way, but of course not all.