To me a Vals is a little bit like a gentle river, you jump into the stream of music and it carries you along. Therefore, it feels best when I can uphold a continous motion a long the line of dance. I’m pretty sure Eider y Luisa Rua would do the same, if they were dancing at a milonga. However, in the vid they do a show and therefor follow more or less the guidelines of stage tango.
Even when your stage is big enough, it makes no sense to dance a long it’s borders in form of a circle. Following the traditional line of dance, half of the time the audience will see only the back of the man – the most unspectacular sight. Hence, the dance pattern is contorted in such a way that the spectators will see a lot of the front and faces of the performers. If you watch the vid closely all figures are aligned for best visibility possible.
Stage and social tango are two quite different art forms in their own rights submitted to very different conditions.