Why Saudi Arabia Is Building a Linear City

In principle this is a cool idea, but it doesn't allow for any expansion. The concept of purpose building a city with an entirely pedestrian surface, a subservice level with shops and a sub-subservice level for transportation is at its core awesome. More places should be doing this. But why a straight line? If you made the "spine" a circle, with spokes that went in and out of the city then you have the possibility of building a second larger spine a few kilometers out and connecting the spokes, leading to essentially infinite expandability. I guess you can do a similar thing with the line as well, by having branches to the line, but I feel like a circular or at least round city with a definitive middle lends itself to human activity. You can make it a cultural hub. This linear expansion exists in several modern middle eastern cities, a notable example is Dubai which stretches for miles along the coast and the city feels very alien and unnatural, with little possibility to explore and check out the area. Whereas some of the older cities which were built around a center, usually a castle, have a much more natural feel to them. Of course these cities are horribly inefficient due to the fact that they are often hundreds of years old and built for populations less than a tenth of what they are now, but a purpose built modern city, with these new innovations, in the style of the old cities would be perfect in my opinion.