They do touch on it in the article. Permits/regulations added to NIMBYs and pre-existing ageing infrastructure conspire to slow things down.

Not to mention political point scoring over large job creation projects. With the rise of robot workers factories such as these might find themselves unwelcome in previously accommodating areas where their size, logistic needs and impact on the surrounding infrastructure were previously offset by job creation.

So at this sort of scale it's as much a question of logistics and impact to the surrounding area as it is one of pure engineering.