I think its because Pritam and Praneet realize that Gautam is serious about the whole things. Other than Puneet, I don't think Gautam will show leniency to ANYONE in the house. Gautam demands perfection. Heck, when he wasn't even captain, he critiqued people's work and tried cleaning it up himself (insects by drinking water/ insects in pool). So if he becomes captain, he will MAKE SURE the house is clean and whatnot. I'm not quite sure what his stand on taking people out of their comfort zones is (Puneet is super big on that), but I think he will definitely kick Karishma out of the kitchen.
Praneet does not like doing certain works. And as much of a hard worker he can be, he sometimes is a kaamchor, or at least it seemed that way when he didn't pick up the kitchen waste until it was overflowing and Gautam called it out. Plus Praneet already DOES NOT like Gautam. I think he can barely stand Gautam anymore and doesn't necessarily make an effort to even humour him anymore. He's only seen with him for P3G I think. So there's no way that he'll vote for Gautam to be captain. Not only would Gautam being captain irk him personally as he does not like Gautam, but it would also irk him due to the fact that Gautam demands perfection.
And honestly, I don't know about Pritam. As funny and neutral Pritam can be, I'm not sure that he's really cut out for a leadership role. He was leader in two different tasks and failed spectacularly in both. Idk. Maybe I'm wrong but I don't see Pritam being a strong leader. I kinda see him as a pushover leader because he gets influenced by certain people very easily (Puneet, Praneet, Karishma). And I think he's also worried about Gautam's perfectionism when it comes to doing house work.
Bollywood
Kyunki Saas Bhi Kabhi Bahu Thi 2
