Is there something like a formula?
I am surprised no one here mentioned age.
Not really. There are recording artists that have had DV cases but are still distributed by major record labels. This just goes to show you that they don't care unless there is a huge public outcry about it.
I have already said that because optics are intertwined with age. The younger the musician, the hotter they look. The older they get the more they start to become less visually appealing especially if they do heavy drugs. BTW, I am saying all of this because sex sells which also happens to be what keeps so many artists relevant to their target market.
Looks mostly apply to female artists. A male artist doesn't need to be handsome. They can also have their face covered in ugly tattoos and it won't be a big deal.