Probably because we do not yet have the mind of Christ, instead we are still carnally minded (minding the things of flesh) rather than being spiritually minded. We ought to be teachers, but cannot because we have not yet "Laid hold of eternal life." We see things, not knowing that were God to rend the veil between the physical and the spiritual planes, we would see just how serious what we do is. Nothing is meaningless.
Do a word study on "Spiritual" or "Spiritually" in the New Testament, I think you might find some interesting answers to your question. So often what people consider "Spiritual" is in fact a carnal doppelganger that we are satisfied with rather than the true spiritual man.
I watched the "Miracle Maker" with my wife last night and found myself really bummed at the part of the movie where it portrayed the discussion between Jesus, Martha, and Mary, because the writers completely took out Jesus' exhortation to Martha. They took out the part where Jesus said that Mary had chosen the better thing. I suspected that it was because of this exact issue you are asking about. People today absolutely cannot stand exhortation. We resent it. May we become a nation of least Priests... Learning the way of obedience through humility. If we learn that, then we can learn the way of Spiritual Exhortation. We cannot learn the way through an establishment of prideful religiosity. I think that we often are on the back-swing because we all have seen so many exhort and condemn when they are in fact not "Spiritual." Satan is so crafty, he plays so many people like flutes in His symphony of carnality through these little games. It is within this context that I would love to quote Colossians 1:9, "For this cause we also, since the day we heard it, do not cease to pray for you, and to desire that ye might be filled with the knowledge of his will in all wisdom and spiritual understanding."
God Bless
-Jer
