Because this is just a fantastic trainwreck on every level.
It's self righteous, accidental NTR where a 30 year old grooms a 15 year old by separating her from her childhood friend, where the author self inserts as the 30 year old.
And from the writing you can tell the author is completely unaware of this and doesn't understand his own creation.
The super low score is probably a spiral where people see a low score, are curious, read it, then give it a 1, and so on. The lower the score gets the more curious people get, because looking at the first chapter and art style, it just screams mediocre instead of catastrophic.