Otherwise England would have been involved in 1996 and they weren't! Had they been though surely they would have atracted a full-house even if the game had been held at Old Trafford not Wembley?
Not that anyone outside the countries involved is that bothered usually, but with little at stake but pride the 3rd and 4th play-off games can sometimes be better spectacles than the finals. In South Africa 2010 Germany beat Uraguay 3-2 in a five goal thriller to make it the 4th time of finishing 3rd. The final in contrast was a tight 1-0 win for Spain against Holland after extra-time.
Given the costs involved using one of the stadiums for another game - especially if it had been in Poland with the final in the Ukraine- would have made economic sense surely? You would have still got a decent crowd especially as it turns out with Germany a beaten semi-finalist and decent viewing figures.
Perhaps somebody out there knows the reason?
Answers on a post card please..