Reason? One of the best songs of Lootera, at least one of the best could-be songs of Lootera, Sanwaar Loon, is sung with lot of irritating mistakes by Monali Thakur, and it reaches the audience like that. Even the title of the song, which should have been Sanwaar Loon, is Sawaar Loon, the former meaning 'I would decorate/adorn' and the latter meaning 'get a rider', if at all meaning something.
This is not all. Bhanvre are Bhavre, Jhonke are Jhoke, Kyoon is Kyoo, and it goes on, e.g. 'Ye saari koyale bani hai aaj daakiya' almost as if the singer got a bad cold while singing.
It's not like we haven't heard such things in the past, but this seems to have happened for the first time with such a beautiful song, a song that could be heard on loop, and remembered for ages, and that is what makes us sad. As for the blame, I'd blame the music director here, as the singer is a newbie, at least to this kind of song, and doesn't boast of Hindi as her first language. But Amit Trivedi is a music director who seems to take every small thing into account, so how he missed the 'talaffuz' in the only version of the introductory song of an Anurag Kashyap movie, is questionable.
Oh, I have beaten the boy to death. But that's the result of killing a must-have-been-a-favorite song. Hope they take care of this in future. Amitabh Sir, I hope you too are listening.