Not everyone has the same opinion lol. For what you find shit or average there are millions that love it. And it goes the other way too. Something you think might be amazing, many others could see as trash. So how is it a huge mystery that something you don't like is loved by others?
KnY's primarily loved for its very endearing characters and the emotional weight they and the story carry. This is helped by its culturally relevant Taishō setting and the personal and relatable themes of the story. Not to mention the high stake fights and the cool powers.
Far better quality swordsmen too.
Virgin Kin emon been around for 300+ chapters, still mid
VS
Chad Rengoku breaking records and hearts in just 10.