Because some of us go to sites like 4chan in order to learn what people
really think. We want to see how they react and what they say when they are protected from consequences by the anonymous nature of the forum. We want the full spectrum of humanity, good and bad.
The opinions of bots are not just irrelevant, they are a form of consensus creation attack. They make it seem like a lot of people have an opinion when the reality might be the opposite. We are not interested in the made up realities that people pay bot operators to create. We want the truth, and the truth comes from real humans expressing their real unfiltered thoughts.