Why did Americans stop using beef tallow and why is it back?

The food preparation decisions that go into the production of deep-fried potatoes at the fast food giant McDonald's have become a source of fresh controversy in the United States. Armed with a controversial theory about the nefarious effects of seed oils on human health, Secretary of Health and Human Services Robert F. Kennedy Jr. recently praised the fast food chain Steak 'n Shake for deciding to cook fries in beef tallow (rendered beef fat). Why did food chains move away from tallow toward other oils in the first place?