Why is it then when the following seven scriptures are read,

that the east is usually understood to be the east part of the Middle East, like areas like Persia, etc.?

Genesis 11:2 And it came to pass, as they journeyed from the east, that they found a plain in the land of Shinar; and they dwelt there.

Genesis 29:1 Then Jacob went on his journey, and came into the land of the people of the east.

Judges 7:12 And the Midianites and the  Amalekites and all the children of the east lay along in the valley like grasshoppers for multitude; and their camels were without number, as the sand by the  sea side for multitude.

Job 1:3 His substance also was seven thousand sheep, and three thousand camels, and five hundred yoke of oxen, and five hundred she asses, and a very great household; so that this man was the greatest of all the men of the east.

Jeremiah 49:28 Concerning Kedar, and concerning the kingdoms of Hazor, which Nebuchadrezzar king of Babylon shall smite, thus saith the  LORD; Arise ye, go up to Kedar, and spoil the men of the east.

Ezekiel 25:10 Unto the  men of the east with the Ammonites, and will give them in possession, that the Ammonites may not be remembered among the  nations.

Matthew 2:1 Now when Jesus was born in Bethlehem of Judaea in the  days of Herod the  king, behold, there came wise men from the east to Jerusalem,

But when it comes to this scripture:

Revelation 16:12 And the sixth angel poured out his vial upon the great river Euphrates; and the water thereof was dried up, that the way of the  kings of the east might be prepared.

That we are told that kings of the east must mean China, etc., the far east?