Simply because,
1. I doubt anybody rooted for AnuKom back then or is hopeful in future
2. I haven't come across any AT for AnuKom yet
3. There is massive fan following for RB
4. AT's made for PreRish
5. War environment between fandoms
6. Some viewers jumping or at least feel like jumping ships
So people are not mad to not realize the difference between a negative character(Kom) and a grey character(RB) and root for RB/PreRish.
Hence I say RB is not a negative character.
Assumptions:
1. AB had to marry Kom due to XYZ reasons which were on the tracks of protecting family and business.
2. P will mary RB for similar ABC reasons, i..e to protect family and business.
3. In both the scenarios AB and P were in love with each other.
so the scenario for AB and P is almost the same right now also and similar circumstances under which PreRish marriage will happen if it happens i.e.
Note: Please no negativity. Only healthy discussions and views. Everyone supports their own favorite characters and please do so. No derogatory remarks for any fandom.