From a few posts back -

"Backing tracks could then lead to 'lip sync' (miming), which is not what audiences pay to hear."

But they do. Most shows by 'big' artists and girl/boy bands, especially those that involve vigorous dancing from the artist(s) are mimed (when did it become 'lip syncing'?).

The bottom line is that there is so much money and prestige tied up in a big show now that artists and organisers can't risk an out of tune, or out of time performance.