Hey SineBricks, thanks for your question.
The answer to this comes in two parts; one is looking at the impact from an organic traffic point of view, which is what the SEO team focuses on, the other is from an internal search and discovery point of view, which isn’t the core focus of the SEO team but still one we look in to from time to time.
So, from a strictly SEO point of view (traffic coming from Google, Bing, Baidu, Yandex, etc) keyword stuffing is a big no-no, it is seen as an attempt to manipulate the search results in a way which may negatively impact the experience of users actually heading to that page. Google have a short explanation here.
With regards to the search and discovery on the markets themselves, this is something we are always aiming to improve. I understand your frustrations with the repetition of target terms in item titles, but have spoken with the relevant team and it is a known issue that we are aiming to fix. For now, we are reaching out to authors who are engaging in keyword stuffing. You can expect more announcements and updates to our guidelines to come shortly.