afaik, it's because Mina is only populated during the Hajj and the temporary structures are deemed enough, while the other structures (additional lanes for the

afaik, it's because Mina is only populated during the Hajj and the temporary structures are deemed enough, while the other structures (additional lanes for the stone throwing, the tunnel or additional levels in the Grand Mosque) are either necessary or still usable outside of Hajj season.