I honestly believe that these differences have multiple causes:
(1) The studio vocals for every single song are perfected with a large number of recorded 'takes'.
Only the absolute best possible vocal performances are used in the final product and of course Madonna and her producers (at least theoretically) have an unlimited amount of attempts to achieve this result. I can also imagine that making multiple demo recordings during the writing and development process of a song on the one hand as a form of practice, but on the other hand also allows a better adaptation of its musical elements such as the melody etc. This allows to music to perfectly complement to Madonna's singing voce.
(2) The studio vocals often act in your head as the base reference for comparison and vocals cords are not yet strained because of the virus.
(3) The studio vocals for every single song are perfected with a large number of recorded 'takes'.
