I think it is important to read the with a prayerful heart, asking God to open our eyes to see the truth God is communicating with us. It is also imperative we read the Bible in context. For example the "100 Scriptural Proofs That Jesus Christ Will Save All Mankind" are taken completely out of context. Remember, the devil quoted scripture when tempting Jesus in Matthew 4:6.
You are correct that God wills (i.e., wants / desires) that all mankind be saved. No one can argue that God desires all to be saved. Why else would He have sent His one and only Son to die an excruciating death on the cross for sin? At the same time, why would He send His one and only son to to die if it were not required to save those who would believe in Him? So what this says to me is that it is God's desire that we be saved and that He's done everything possible to save us, excluding forcing Himself on us and providing absolute undeniable proof because that is not love and would not require faith which is the basis for salvation. The problem is we haven't done our part to come to God. He didn't leave us, we left Him when we ALL sinned. Therefore, He made it possible for us ALL to be saved. Unfortunately we're not all going to accept His plan for saving us and some will spend eternity in Hell.
Second, God doesn't owe us anything. Never has, never will. But because of His love He gives us stuff we do not deserve. Who are we to question the one who made us? Check out Romans 9:19-21
Third, I think we humans often have a misconception of God. God is holy, loving, and just. Because of God's holiness, He can not (i.e., not will not but can not) tolerate sin. Thus sin must be punished; it's why all of us deserve to go to Hell. However, God's love provided a way out through His sinless Child who came to Earth as a human and suffered the penalty for our sin. In order for us to avoid Hell, we must accept that salvation (i.e., it is not automatically granted to all of us). Romans 10:9 tells us, "That if you confess with your mouth, 'Jesus is Lord,' and believe in your heart that God raised Him from the dead, you will be saved."
I suggest reading the following articles carefully and also the versus mentioned in the above posts in context using several Bible translations (e.g., NIV, KJV, ESV, and NASB).
How can a God of love send anybody to Hell?
Will all mankind eventually be saved?
Is God biased? Is it fair to save only some?
Salvation Through Christ: A Matter of FAITH
Finally, check out the "The Problem of Pain" book by the gifted C.S. Lewis. C.S. Lewis has an intriguing life story.