The tongue of a cat, like other animals, contains receptors on it. These receptors register different tastes. For example, humans have receptors that lets them distinguish between such tastes as bitter, salty, sour, savory (umami), and sweet.
Cats, including the domestic cat (Felis silvestris catus), are believed to be the only animal that is unable to taste sweetness. believed to be the only animal that is unable to taste sweetness. Researchers encoded the DNA and found that cats lack two genes known to encode the ability to taste sweetness: Tas1r2 and Tas1r3.
Cats are obligate carnivores, which means they require meat for all of their nutrition. The taste of sweetness is an indicator of rich carbohydrates, something absent from the natural animal-based diet of cats. The genes for tasting sweetness were turned off in cats millions of years ago. The need to sense sweetness is not a necessary function in an animal that doesn’t need to consume high nutrition plants.
Even cats that like to eat ice cream (not something recommended as part of a healthy cat diet) are not eating the desert for its sugar, but attracted to the fat.
Li, X., Li, W., Wang, H., Bayley, D. L., Cao, J., Reed, D. R., … & Brand, J. G. (2006). Cats lack a sweet taste receptor. The Journal of nutrition, 136(7), 1932S-1934S. https://doi.org/10.1093/jn/136.7.1932S