Perhaps the story is set in a chaotic or dystopian world where memories are easily lost or manipulated. Or, it could be a plot device to make the character feel isolated and drive the story forward.
Well, it might be that the story has some sort of mind-altering element that wipes people's memory of you. Or maybe it's a test for your character to overcome this lack of recognition and make a mark.
Perhaps it was overshadowed by other more popular novels at the time. Or, its themes and storylines were too niche to capture a broad audience's attention and memory.
It could be that the world in the light novel is too big and chaotic, and people have their own concerns and distractions. So, it's easy for them to forget about you. Also, if your character doesn't have standout qualities or actions, it's harder to be remembered.
The 'Why Does Love Do This to Me' manga might have a big impact due to its ability to touch on universal themes of love and heartbreak. It could present these themes in a way that's both realistic and captivating, drawing readers in and leaving a lasting impression.