In certain clothing categories, there are so many false results that it is very difficult to find what you want. Customers are unwilling to sort through hundreds of dubious results, and this is how they are trying to curb the problem.
I went to buy a hooded animal scarf for my daughter before Christmas, looking for a specific brand. There were literally hundreds of results, only a few of which were the brand I specifically searched for. Part of the problem seems to be that the vendors add popular keywords to items that only sort of fit the description in hopes that you'll see and buy their product.
I suppose that Amazon could police keywords, but then they'd end up arguing with vendors over the definition of what "is" is. This seems like a more even-handed way to fix the problem.
Customers won't stick around if it takes them hours to find a product.
If this was the case, I would think the problem could be solved by keyword categorization.
I have a shop on Etsy and I know that they do police the tags and the other Etsy members will report a shop if the items are mistagged.
Good point!