Why do amazon hide some seller listings from search results?

We have recently noticed that amazon intentionally hide some listings from natural search results. To find this out, we simply searched for our product using keywords from the product listing title, and then filtered the results by price in ascending order - we could not then see our listings (we were searching from the main search bar in “all departments”)…

We have raised this with amazon and just had it verbally confirmed that they do indeed hide some listings from search results - the person I spoke with was quite ambiguous about why but one thing she did hint towards was “sales velocity” - this doesn’t really make sense though, as surely if they don’t display your listings then you will never achieve any sales velocity so its a catch 22 situation.

It’s a little concerning that amazon don’t display all listings and make it a fair playing field for sellers/merchants.

Does anyone else know more about this topic and why amazon purposefully hide listings - without actually giving sellers any warning?

PS. The products themselves are all “active” listings without errors and warnings etc.

Many thanks