The Reason is related to much deeper

Steely Dan´s twosome fell in heroin, but survived.
They `fell ill´, such as Donald Fagen said.

Band members can stop an individual spiralling into self-destruction, Honey Langcaster-James, `celebrity psychologist´ , says to BBC.
She believes the support of a band may be protective. I think this it part of survival, if individual self has willing to do it, and man survives his life.
Like Bruce Springsteen said primrose path is always open, and attracts a man.
Also every reason, from which Honey Langcaster-James makes a list, are the truth.

Still, I suppose, that she himself is not top-level talented, and she has not occurred so on the stage. If not. Man  did not know, what is the feel the collective consciousness; One in which works a dialogue between the artist and the audience.
From such state of mind like some drug´s effect, by after, going in to the recovery, is named of post-traumatic stress disorder.

According the source, they can find themselves in a situation where everyone around them are paid employees - the PR guru, their manager - all interested in them from a financial point of view and not in their personal needs - it's hard for the artist to know who to trust.

This is a pretty common to almost all self-employed.