It is very simple.
BB wants to ensure Sushant is gone after he showed attitude during the task and also Salman bashed him and said your attitude is not working. So, Sushant has to go..
Now despite people shouting that the voting does not matter, it always matters. As I have said number of times the channel always eliminate the person getting lest votes.. they can not do otherwise but what the channel does is to manipulate the nomination and edit the 45 minute coverage and gives less footage to the contestant they want to go..
If Suahant is against any of the guys in bedroom gang, Sushant has a strong chance of survival since the bedroom gang will draw no vote.. Diandra, Karishma.. are at equal risk of getting eliminated.
By nominating the stronger group, BB ensures that Suashant is up against the heavy weights and surely will be eliminated.
Elementary..