Has it occurred to you, Fran, that many of these 'celeb' singers do this precisely because it IS getting harder and harder for them to sit in with any bands that CAN play their material decently?

Back in my day of cabaret backing, they merely turned up with charts, and expected the band to be able to play them well. Perhaps now, when half the time they turn up at places that don't even have a real band, just some kind of karaoke act masquerading as a band, it is merely more expedient for them to provide their own tracks? Expecting the house act to be able to really play seems rarer and rarer...