God doesn't perform parlor tricks on a whim because:
1. the necessity of His existence is so apparent that rejecting some sort of God is pure logical fallacy.
2. as stated before, God is God, and, like it or not, you are His creation.
Take this analogy for example:
A rich man sees a beggar on the street. The rich man decides to aid the beggar in life. The rich man promises to give the beggar 100,000 dollars and 30 days worth of food. The rich man says, "If you want more, come work for me in my estate. There, I promise you, there are more rewards for your service." The beggar, however, is not ready to work and declines. The rich man, not distraught, promises to return a month later, with the same amount of supplies and the same offer.
The beggar manages to secure a house and lives comfortably for a while.
As he said, the rich man returns a month later. The beggar, wanting more than what was offered, says, "Give me 200,000 dollars and 60 days worth of food." The rich man says in reply, "I am happy to give you even more than this. However, I do not want to spoil you and make you lazy; you simply just have to work for me and everything will be given." The beggar, however, refuses to work and demands his increase. When the rich man refused again, the beggar storms off. The rich man sets 100,000 dollars and 30 days worth of food in the beggar's house and leaves, determined to come back again in a month.
I can't believe I used a corny parable to illustrate a point; sorry about that. However, the meaning remains the same. I hope you can pick out the lesson within; i will explain if need be.