I think it's more likely that they've A/B tested faulty algorithms and picked the one that's the least faulty.

I don't have proof, but I strongly believe that a search algorithm that returns what a customer is actually searching for will drive more sales. I suppose it's possible that with time, consistently bad results will beat a customer into submission and drive more sales of stuff the customer doesn't want. But I don't believe that's true, and this would only be the case if the customer accepts that the thing they want doesn't exist. If the customer is pretty sure that solid color shirts exist, they'll just shop elsewhere until they find it.