My parents did it to draw scrutinty away from their own shortcomings.
Rock stars are easy scapegoats. It's much easier to simply blame a rock star for a child's shortcomings rather than plan a weekend camping, skiing, or beach trip; Which is the kind of attention children really want from their parents. I think this is probably human nature and possibly a comment on our times.
We should all try to take responsibility for ourselves and try to lay less blame on rock stars. As parents we have the duty to offer our children something more appealling than what rockstars offer. It's a tough sell sometimes, but it is far from impossible.