God saving men through dreams?

Why doesn't the Lord reveal Himself to people through dreams to tell them to believe in Him, especially in places like Asia and the Middle East?

The Bible teaches that though the Lord used a variety of methods to reach the world in the past, today the Lord uses His word to reach the world with the truth of the Gospel:

Heb. 1:1 God, after He spoke long ago to the fathers in the prophets in many portions and in many ways,
Heb. 1:2 in these last days has spoken to us in His Son, whom He appointed heir of all things, through whom also He made the world.

Paul echoes this truth in Romans and in 1Corinthians:

Rom. 10:17 So faith comes from hearing, and hearing by the word of Christ.

1Cor. 1:21 For since in the wisdom of God the world through its wisdom did not come to know God, God was well-pleased through the foolishness of the message preached to save those who believe.
1Cor. 1:22 For indeed Jews ask for signs and Greeks search for wisdom;
1Cor. 1:23 but we preach Christ crucified, to Jews a stumbling block and to Gentiles foolishness,
1Cor. 1:24 but to those who are the called, both Jews and Greeks, Christ the power of God and the wisdom of God.

1Cor. 2:2 For I determined to know nothing among you except Jesus Christ, and Him crucified.
1Cor. 2:3 I was with you in weakness and in fear and in much trembling,
1Cor. 2:4 and my message and my preaching were not in persuasive words of wisdom, but in demonstration of the Spirit and of power,
1Cor. 2:5 so that your faith would not rest on the wisdom of men, but on the power of God.

The Bible teaches that the Lord used lessor methods to reveal Himself in past times (i.e., prophets, dreams, etc.) as a temporary measure until the arrival of His Son Jesus Christ. Once Christ was revealed and the canon of scripture complete, the Lord relies exclusively on the word of God.
And the Lord is fully capable of bringing His word to everyone and anyone as He chooses. The Lord will not leave any of His elect behind, as Jesus said in John 6:

John 6:37 “All that the Father gives Me will come to Me, and the one who comes to Me I will certainly not cast out.
John 6:38 “For I have come down from heaven, not to do My own will, but the will of Him who sent Me.
John 6:39 “This is the will of Him who sent Me, that of all that He has given Me I lose nothing, but raise it up on the last day.
John 6:40 “For this is the will of My Father, that everyone who beholds the Son and believes in Him will have eternal life, and I Myself will raise him up on the last day.”

On occasion, we have heard reports that the Spirit is still using dreams or other means to draw men to Him, especially in Asia and the Middle East. These experiences appear to be limited to areas where the word of God is not yet easily available, and so the Spirit must use other methods as a temporary measure. Nevertheless, these experiences are always followed by the introduction of the word of God, so that the person may gain the full counsel of Christ by His word.

We advise you to be cautious when dealing with any report of a so-called prophetic dream or revelation. Often these reports are not credible or find their source in demonic activity. Even when the Lord may be using dreams to draw unbelievers to the Gospel, these measures are not a substitute for the word of God.