Why on Earth would we want a rail connection to the UK? If we were going to go through the trouble of building such a megastructure, surely we'd go the extra cm

Why on Earth would we want a rail connection to the UK? If we were going to go through the trouble of building such a megastructure, surely we'd go the extra cm on the map and connect to mainland Europe? Not that we need that either, or want it, but even in the fever dream this article presents, this doesn't make sense.