lip sinking on live TV

So, over Thanksgiving I watched the Macy's Thanksgiving Parade. I noticed that all the musical acts all were lip sinking, because their songs had back up singers or an instrument that was not with them on the float. In years past I had noticed this. Tonight I am watching the Christmas In Rockefeller Center Christmas special. This is on every year as well. I noticed that many of the artists were lip sinking. I noticed this after Boys 2 Men had finished and Charice took the stage after them. The song was cued wrong. It was cued to the song previously, so it was obviously that they were both lip sinking. So, it got me thinking, why do they do that? As well as, do any artists on TV do anything live, or is it all pre recorded? As well as why is this?? Just an observation I thought I would share.