It was built because some people had a whole lot of time on their hands, and they wanted to play dominoes with the gods.
The first, if you build it, they will come.
It was built by the guberment at the time as the first link to the cross channel bridge. The guberment figured out it is easier to build the first part of the bridge on land cause it was easier.
With cost over runs and miss management no more was built.