Historically weight as an idea existed long before there was clear theory about gravity, an understanding of what a force is and the distinction between mass and weight.
Since then, and possibly also for the same reasons given above, there isn't a single fully defined meaning of weight, even within different areas of science / engineering. For instance, some say an object in freefall or orbit still has a weight of mg, and others say it has zero weight because they effectively define weight as what reading would show on scales placed under the object. And I have a feeling there is a third distinction too but I can't remember it. Bear in mind that these different uses are not mistakes, they have just chosen a usage of a word to be the most helpful in their own field.
Also, if someone asks about the weight of something and you give them an answer in kilograms or grams...