You must have some sort of poisoned history with amzn. I just tried what you describe, and it works perfectly.
All four of those non-Adidas hits are "Sponsored" results, but that's not particularly easy to notice (for one of them it's almost impossible).
I would agree with GP that Amazon product search often leaves much to be desired. It's hard to search for X without getting accessories for X, competitors to X, products that can be connected to X. This is annoying at best, and crippling if you want to, say, sort by price (all the cheapest matches will be accessories or otherwise not what you wanted).
Now that Amazon has captured user-share, they will (ineluctably) abuse user good-will (by padding search results with ad-placed products the user does not want) until they reach some marginal breaking point. The users that remain are either oblivious or cursed with a lingering taste of bad-faith and bullshit.
Eventually the giant will strangle itself in its sleep, but that's probably 50+ years out given how these things go.
I can see (because I was there discussing it back in 95) what the appeal of personalized search results could be for both sellers and consumers. But a few decades of that BS have fairly convincingly made the case that it is a horrible idea.