Why do the Buddhists say that God (Krishna) really does not exist? They say that only emptiness exists, and nothing else. Is emptiness the highest truth?
Answer: If It Were, You Would Not Be Inquiring
If emptiness were the highest truth, you would not exist to inquire about emptiness, nor would I exist to answer your question about emptiness. If all was emptiness, how could the Buddhists say that all is emptiness? There would be no Buddhists and thus no one to say that all is emptiness. But there are Buddhists saying that all is emptiness. Therefore their assertion is itself proof that their philosophy is absurd and thus invalid. Emptiness cannot make assertions.
The reason that in this material world people often deny God's existence using various philosophies such as the Buddhist concept of emptiness is that we all came here to this material world because we were envious of God's supreme position. Therefore it is natural that people in this material world will often deny the existence of Krishna or God.