1. God does not heal everyone because some people believe when they see miracles.
Then many (not all) of the Jews which came to Mary, and had seen the things which Jesus did, believed on him. John 11:45
2. God does not heal everyone because only a few people believe in God when they see miracles.
But though he had done so many miracles before them, yet they believed not on him: John 12:37
It would be nice if there were many more miracles but the fact is that miracles are only going to add a few more people to the faith. Some people do not believe no matter what they see. You can raise the dead in front of them and they will still not believe.
Abraham told the rich man: “…If they hear not Moses and the prophets, neither will they be persuaded, though one rose from the dead” (Luke 16:31).
In fact, some people will hate you because of the miracles they see.
Then again the Pharisees also asked him how he had received his sight. He said unto them, He put clay upon mine eyes, and I washed, and do see. Therefore said some of the Pharisees, This man is not of God, because he keepeth not the sabbath day. Others said, How can a man that is a sinner do such miracles? And there was a division among them.
They say unto the blind man again, What sayest thou of him, that he hath opened thine eyes? He said, He is a prophet. But the Jews did not believe concerning him, that he had been blind, and received his sight, until they called the parents of him that had received his sight. And they asked them, saying, Is this your son, who ye say was born blind? how then doth he now see? His parents answered them and said, We know that this is our son, and that he was born blind: But by what means he now seeth, we know not; or who hath opened his eyes, we know not: he is of age; ask him: he shall speak for himself.
These words spake his parents, because they feared the Jews: for the Jews had agreed already, that if any man did confess that he was Christ, he should be put out of the synagogue. Therefore said his parents, He is of age; ask him. Then again called they the man that was blind, and said unto him, Give God the praise: we know that this man is a sinner. He answered and said, Whether he be a sinner or no, I know not: one thing I know, that, whereas I was blind, now I see. John 9:15-25
The miracle Jesus did brought about a surprising division. You would have thought that the healing of a man born blind would make everybody believe.
If God was trying to make everybody believe by miracles then He failed. No matter what God does, certain people will never believe. God is therefore not in a hurry to heal everyone.
I know a man of God who had a halo appear over his head when he was preaching. Do you think that everybody believed in his ministry? Certainly not! We must understand then that miracles or no miracles, the work of God still goes on. Only some people will believe because of the miracles.
This explains why one of the greatest evangelists of our time, Billy Graham, could preach the gospel without praying for miracles. People are saved by the foolishness of preaching and not by the power of miracles.
For after that in the wisdom of God the world by wisdom knew not God, it pleased God by the foolishness of preaching to save them that believe. 1 Corinthians 1:21