Thankfully none of them can get around actually having to sing if there just some fake creation they disappear eventually like eighties leg warmers or shellsuits, Take That and Westlife whatever you think of there music etc at least they can sing.
I've come under the impression that if a band doesn't write all thier own music and can't sing it well, they eventually die off. For example, if you can write your own pleasing music you can carry on when a fan base that grows up and on to other performers while you continue to acquire new fans. If your stuff is written for you, the writers might move onto other 'talent' when your fans start to lose interest. It also helps to evolve with the times. This isn't 100% accurate, but might hold some water when discussing hugely popular yet short shelf lifed musical artists.