In Spain, the affairs of the gridiron is often intersect with political matters. Just because Barcelona and Athletic Bilbao who advanced to the finals, Madrid is reluctant to make room for these two areas of political opponents.
Also presents the final of the Catalan and Basque, and the political factors above, the Bernabeu was considered 'haram' to wear both. But until now, I have found no decisions that come out of the meeting RFEF and Madrid.
As described above, Atletico came up with a fairly neutral alternative. Moreover, the venue will still be held in the capital, Madrid and will be considered good for the RFEF, Barcelona and Bilbao.
