What is the point in this forum if everyone gets red/negative trust?
You are encouraging people to invest into this kind of websites in the second part of your post.
Why don't mods just remove it and ban hyip altogether?
Trust isn't moderated (excluding extreme cases of abuse). Why 'HYIP' isn't going to be removed is fairly complex question to which I can't provide an answer to. IIRC sometime in the past this section didn't exist.