But they kind of are (a cult band). Most people in the world know Metalica while hardly anyone ever heard any of the Sisters Of Mercy's tracks.

Normal people don't care- they just enjoy a ballad or two.

I've long since learnt to separate an artist from their art- a fair share of the musicians, actors, directors etc aren't really a decent bunch

Not really, they missed that chance when they released Load and Reload and who knows what they did after that. I got fed up with their foray into commercial music and moved on to prog metal and other more interesting stuff. If they had stopped after the black album or continued to release quality works, then things would be different, but they chose money, whining, lawyers and drunk teenagers as an audience. They became lame and popular, which excludes being a cult band. Cult bands are not very popular in fact, as you have yourself pointed out.