Because “value” in the economic sense is not synonymous with “value” in the ethical sense and neither is it a complete overlap with “value” in the way we use it in everyday speech.
In economics value is about choice and indifference. If you have two options and you are indifferent between them they have the same value. Everything about value in economics flows from there. It’s a very useful concept. But it’s not the same as “value” that a philosopher, a poet, or anyone else might talk about. Similarly “utility” in economics is fairly much equivalent to value in economics — but “utility” in economics doesn’t quite map to the common term “useful”.
In economics value is about choice and indifference. If you have two options and you are indifferent between them they have the same value. Everything about value in economics flows from there. It’s a very useful concept. But it’s not the same as “value” that a philosopher, a poet, or anyone else might talk about. Similarly “utility” in economics is fairly much equivalent to value in economics — but “utility” in economics doesn’t quite map to the common term “useful”.