The pigment is cheaper, it's not toxic, and the colourman can point to the ASTM rating in order to sell the product easily. It's unfortunate that I have samples of Naphols that have faded in a matter of weeks in normal lighting and completely when mixed with zinc white. Natural madder is even worse. They are significantly more permanent than Alizarin, but perhaps not quite permanent enough to be called permanent. And, their properties are not often similar.
Insoluble mercury is a whole different matter.
I haven't died yet. And, some have said that dentists are scaring people in order to get them to come in and get them all replaced. The source you posted is similar to those I have read. Organic mercury is extremely dangerous, yes. I've said that.