Sure, but the serving size can vary, even between different package sizes of the exact same product, and certainly between different manufacturers.

Overall, humans are dumb and can't (or won't) do math in their heads. Consider the stupid thing with the failed 1/3 lb burger positioned in the market against the 1/4 lb burger ( https://www.snopes.com/news/2022/06/17/third-pound-burger-fr... ).

If one product says "5g fat / serving [serving size: 40g]" and another says "4g fat / serving [serving size: 30g]", many many people will think that the second one has lower fat content.

If these were normalized to 100g, it would be clear that the first has 5/40*100 = 12.5g of fat whereas the second has 4/30*100 = 13.3g of fat.