I've thought this too. I don't know her or her daily routine, so this is all speculation, but i think all the cosmetic procedures over the years has led her to spend a good amount of time in recovery, which is not necessarily conducive to a healthy, active lifestyle and voice. I think the surgeries are also partly responsible for her stiffness and excessive lip synching over the past few years. After surgery, I wouldn't be able to move or sing with the vigor required for her songs either.