Then you wouldn't exist. Even the smallest business goes through years of losses before it (hopefully) reaches profitability. Pay to sell is the only way nearly 100% of incumbents have to simply exist. If they don't do it, someone else will

Traditionally, businesses build a reputation and customers learn where to find them (a physical location). They then become and stay profitable. Anyone depending on a monopolist for its pay-to-sell strategy won't usually reach profitability. The monopolist might be as small as a greedy feudal lord in the middle ages. Today we have Apple/Google etc

There is a real difference between starting a business and running it at a loss before reaching profitability and consciously entering a contract, where you know you are producing at a loss ( and your contract partner benefits ) that only furthers your profitability gap. If this is the opening bid, it is highly unlikely it will get better. If anything, it will only get worse. You don't make it up in volume when you sell at a loss already.

<< If they don't do it, someone else will

That is the interesting part. The pressure is so high that people are willing to forego their own self-interest and basic critical thinking skills, because someone will do it at or below cost anyway. It is great for Walmart, but it would explain why so many businesses fail so hard. They are way too nice to the other party.

Not enough profit is different from loosing money.

Here the vendors are simply making less money because their product is part of a highly competitive marketplace.

Not enough profit is the main reason to shut down a business, unless you have a good and realistic plan on how to reverse that. All that effort and all that risk can be put into more lucrative ventures.

Not enough profit is different from loosing money.

Here the vendors are simply making less money because their product is part of a highly competitive marketplace. Furthermore, their position is weakened because they are poorly differentiated from their competition.