Maybe we doubt this and seek to hold on to the many Christian institutions that have been founded with clear intent to change society. Whilst I would not question the sincerity of those who founded them and those who work in them now, the least association with any of them will show us that they are prone to fall into the trap of becoming mere man-made organisations, incapable of fulfilling the vision which which they were founded.
The Lord Jesus does not look to us to get the world sorted out before he returns. He looks for the Church to have made herself ready, like a bride for her bridegroom. Only when he returns will the kingdoms of the world become the kingdom of God and of his Christ.