So the reason is revealed... The reason behind the distance between Buddha Bajaj and Kuki is the fact that Buddha Bajaj is the fact that he can't sort his own issues out. Buddha Bajaj had issues with his wife - she cheated on him. He can't get over himself and takes it out on his daughter, who is just craving for love. He gives his "love" and shows care to other people but can't show even a bit of affection to Kuki. These are like the typical narcissistic "progressive" men who taunts their kids with stuff like apne maa par gayee hai.
This is so much so that Kuki is afraid to even begin to tell him the truth. Buddha Bajaj hasn't taken the time to build a relationship with his daughter because he's too busy in doing Prerna ji aap bohut strong ho, so I don't get why he's angry that she didn't tell him anything. For Kuki to be able to trust him even a bit, it takes nuturing and care, along with scoldings. What Buddha Bajaj has done is he's just given the responsibility of his daughter to Prerna and exempted himself from his responsibility as a father.
It's just plain sad that Buddha Bajaj takes out the anger directed towards his ex-wife on his daughter, who isn't responsible for the situation at all. This is the same person who said he would be a father to Sneha. If he takes out his ex-wife's issues on innocent Kuki, how does he expect that he can be a good father to Sneha???