I have done some research and found out why you think Jesus did not die for everyone.
Attempting to use John 11:51-52 (an entirely different book) as the basis to make the "World" refer to Gentiles.
But, in the same book, John writes 1 John 5:19,
We are of God and the whole world lies in wickedness.
So he is saying that unregenerate people are the world.
Monergism vs synergism
Monergism says that it is all God and none of man.
Synergism says that man must cooperate with God to be regenerated.
Throughout the Bible we see God giving man a choice, obey and be blessed, disobey and be cursed.
In Psalm 32:8-10 God says
32:8 I will instruct thee and teach thee in the way which thou shalt go: I will guide thee with mine eye.
32:9 Be ye not as the horse, or as the mule, which have no understanding: whose mouth must be held in with bit and bridle, lest they come near unto thee.
32:10 Many sorrows shall be to the wicked: but he that trusteth in the LORD, mercy shall compass him about.
Here He is telling us we need to make the right choice.
Then In Isaiah 1:18 He says, Come let us reason together, though your sins be as scarlet they shall be as wool,
though they be red like crimson they shall be white as snow.
Our part is to say yes or no, once we say yes God takes over and does His part.
All glory goes to God, we get no glory whatsoever.
He did all the work, all we did is give the go ahead.
I will glory in the cross, not my agreeing to God.