In the wild, they obtain the plant-based substances exclusively from the stomachs of their prey. Now you could say: "It works with dog food too - without any meat and with lots of eggs, vegetables and dairy products. However, this cannot be applied 1:1 to cats.
Dogs are omnivores and can utilize plant-based food well. Yes, even wolves eat fruit. Unlike dogs, cats have always been pure carnivores. The cat's entire system - from teeth to digestion - is designed for animal components.