They usually replace them with interesterified fats which are even worse.
Fats go rancid fairly quickly. The industry needs stable fats, unfortunately this is done through manipulation of the chemical structure.
Fats go rancid fairly quickly.
Polyunsaturated fats go rancid quickly. Saturated fats do not.
But, of course, the industrial seed oils we get out of corn, soybeans, cotton seed, etc., are polyunsaturated. Saturated fats come from animals and tropical fruits - lard, beef tallow, coconut, avocado, and palm kernel oil.
Industrial seed oils are far cheaper to produce.