That’s not what those statistics show. All they say is that for out of 19,700 people with a bachelor’s degree in agricultural or food sciences, about 2,800 of them have a occupation in the same broad field. But those statistics don’t intimate anything else - there’s no reasons given. The rest of those agriculture majors may have non-agriculture degrees because they voluntarily chose to leave agriculture, because they are applying the knowledge from their degrees in ways that aren’t considered “broad field” by the NSF (like working as a manager in a food sciences company), or for some other reason.
Also, if you look down the list, there are few STEM majors in which people are directly working within the broad field.
Sure, except 1) the OP did specifically mention the idea of double majoring in agriculture and economics, strongly implying that they wanted to do something involving both of those fields - agricultural economics and/or agribusiness was a natural conclusion to draw and 2) the implication was also that unless the OP’s family had a farm then an agriculturally-related major might not be a great idea, which I think is is a bit narrow. Agriculture is about way more than being a farmer, specifically. And it’s about way more than producing food.