A very important detail:

maintaining that their products can be handled safely if the proper precautions are followed. But growing evidence shows that the dust generated when cutting or polishing artificial stone is so toxic that it can sicken people at sophisticated fabrication shops following Cal/OSHA’s current rules, which prohibit dry cutting of the material and require advanced respiratory protection.

Previously, the claim was that the workers were harmed because they weren't following safe handling practices. This indicates that's not (entirely) the case, hence the ban.