The search ads ostensibly solve the cold start problem: If a seller introduces a new product, how is that to be ranked? Well, they can buy some ads, get some ratings, and boot up their sales & search ranking. Great.

It of course also creates essentially perfect competition. Amazon will even tell you the top selling products across categories, so that no seller can make excess profits for long - others will quickly jump into the fray to compete that away.

This is of course the market working as intended - the sellers compete away any and all surplus. Normally that would be a good thing for consumers! Unfortunately the search ad tax is very real, and siphons off a good chunk of the surplus as monopolist rent.

This is all structural. A marketplace like this is a natural monopoly with massive network effects. And the allure of the search ad is irresistible - they literally can't not do it, lest their shareholders rebel.

Google ads work exactly the same way.

As a seller your only options are to either have better conversion economics than the competition (so you can win the ads bidding war - guess why every successful site on the internet is gameified to all hell, and why the amazon listing titles & descriptions look like they do) or to not play.

If you can create a viral hit for a product you can probably eke out excess profits for a few months - people want precisely your branded product and not a cheap knockoff, at least for a while.

("Excess profits" = anything above what will literally make the marginal seller say "it's not worth it", which is a very low bar when competing with the entire world)