Supporting characters can add depth and complexity to the story. They might provide unexpected perspectives or trigger important events that shape the narrative. Also, they can make the world of the web novel feel more realistic and immersive.
Because they often play crucial roles in driving the plot or influencing the main characters' development.
You shouldn't underestimate them as they might have hidden backstories or skills that come into play later, surprising the readers and adding twists. Sometimes, it's a supporting character's actions that lead to the climax or resolution of the story.