Did Virat ever consider if he had to do household chores when he was studying in college or doing ips training? When he didnt do it, why should Sai?? Just coz she has married and has responsibilities Sai has accepted it and Virat also "expects" it. sai does it more out of feeling indebted. she cant stay for free nah. Its like she is a PG/tenant but unfortunately for them she has the title of virats wife. So she is not "paying" to live and eat there but no one considers her family either. Also Virat is not factoring in that she is not a stay at home bahu who has time to do these things like pp or karishma. In that alta episode he said ghar ki aur bhi bahu kaam karti hai, so ghar ke kaam karne seh naukrani nahi ban gayi and Sai very aptly replies saying that she is NOT considered a bahu or family by them and no one does baat baat peh beizzati for other bahus.
I think one more reason mohit has judaav with Sai is that he has also been treated with same disdain like Sai is, like a second class citizen. He has done odd jobs in thr house with no appreciation unlike ghar ke chirag Virat and Samrat. He is actually emotionally invested in all the family members- devi, Ashwini, samrat, virat but no one pampers him. if you see, he cares deeply for everyone. He gave devi a hug, he wanted to do preparation for harinis bday, he was there to condole ashwini many times. And even for Virat. When Virat was dejected about Sai not returning he was there to suppprt him too. The brotherly bond of jeeva shiva is glorified but theres no emotional bond shown between Virat/mohit. Apart from that one hug when mohit was denied food- that also because Sai stood up. I dont think virat would have reacted if he had been there and Sai wasnt. Because mohit ke saath aise bartaav humesha hota tha.