Because you take sweet ultraprocessed food since your a baby. Then, children don't like veggies.
In the wild where the immediate pressure is on getting enough calories and macronutrients while lack of micronutrients only cause problems in the long term, any human wasting energy collecting and digesting food that doesn't have calories and macronutrients (vegetables) would be quickly weeded out.
Look at the nutritional information of any vegetable for yourself. Fruits, nuts, legumes, grains, potatoes etc all come with the fiber, vitamins and minerals that misinformed people think can only come from vegetables while also being loaded with calories, protein and essential fatty acids all which are pretty much completely lacking in vegetables.
It's simply good enough for humanity to survive without having to evolve a more accurate taste organ.
I think using palatability as a way of measuring nutritional quality is not going to help you in the context of a society raised on ultraprocessed foods, because sugar, salt and other chemicals give taste to food without giving it nutritional value.
If vegetables don't give you as many calories as meat and as you say: "...any human wasting energy collecting and digesting food that doesn't have calories and macronutrients (vegetables) would be quickly weeded out", why there are so many animals still alive after millions of years eating plants (some of them eating many kilograms every day)?
Sugar contains a lot of energy so it's not fooling you when it's tasting great.
Can you say which specific animal is alive eating food without much caloric content (and which specific vegetable are they eating)?