Why Kumar Sanu & Alka Yagnik Lost Their Voices?

Many times or most of the times they sing off key in live shows and with change voices why is that their voices got affected by age but at the same time asha bhosle and lata mangeshkar or even Sp bala had perfect pitching , Asha and Lata still are in pitched

Yes especially seeing them live in concert the change in their singing is obvious ! Sometimes i think if they don't practice as much as before then it happens also age has it's factors too.. some still sound the same even in older age which is amazing.

The mirchi lagi 2.0 was so bad.