IF you’re actually curios, it was because we used to import them, and the importers would dye them red due to discoloration in how they were harvested. Domestic production ramped up in the US and since pistachios didn’t have to travel as far, and because modern harvesting was more mechanized. It was easier to wash, dry, roast and salt them in a shorter time period avoiding the discoloration that required the dye in the first place.

So instead of dying them back to green they chose to make them unholy abominations made with red dye that is known to give cancer? Cool.