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. When there are examples of bright red Vermilion on paintings that are hundreds of years old and I have Naphol paints that fade in a few months or even weeks, I am less inclined to blindly trust ASTM ratings. Alizarin Crimson is one of the biggest failures in this regard as apparently it will fade in light tints and glazes even in the dark and this is hardly news. Yes, Alizarin is certainly the most popular fugitive pigment.
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. No it is not, do your research. Insoluble mercury is a whole different matter. I haven't died yet.