Just because we don’t know the reason they made the change to maize doesn’t mean it wasn’t valid.
Amongst other possible problems, goosefoot can cause hayfever like it’s relative ragweed.
I can’t speak for most of the crops listed, but I do have experience with members of the Chenopodium genus. Corn is a lot less work!
The researcher in the article compared yields, but not the man-hours needed to get it from the field to the dinner table. Corn doesn’t need threshing or winnowing, and you’re a lot less likely to end up with a ton of chaff in your lungs.