did some digging on this, it seems that salt is refined to improve its storage, basically, refined salt can sit on the shelf forever.
Also, if the salt is taken from a polluted area, the refining process, to your point, will remove some not-so-good elements, e.g. toxins associated with the salt. And an all-white salt product will look “purer” to the consumer and, therefore, might increase sales.
Unrefined salt becomes more and more popular as people tend to move towards "natural" product.