So if Adam caused all to sin and "die" why does not the second Adam cause all to live - i.e. universal salvation?
For the very reason that to come to new birth, to be born-again, one must place faith in Christ, believe in the Son of God. Where as Adam's sin condemned all men, Christ's sacrifice has made available to all men salvation. However, this righteousness is one of faith, and in so doing (placing faith), one then becomes a child of God by the Spirit of Adoption (the Holy Spirit). So it is not that Adam is greater, it is that God requires faith. Jesus
is the propitiation for the sins of the world (all of them), yet to receive this forgiveness one must believe the Gospel.
The check is there, people need to turn it in. In other words, salvation is available to all (its universally available to anyone that would believe). Yet not all universally accept Jesus Christ as Lord and Savior and believe what He has done, rather they want nothing to do with Him or have confidence in self.
Universalism is a false doctrine, and while it may seem merciful it is tyrannical. God doesn't force people to love Him, He simply grants the invitation. Universalism presupposes that it is more merciful that all would be saved, and indeed it is God's desire and yet one that He will not have, sadly. He cares for all His creation, but not all of them will be saved for a number of reasons which ultimately tie into rejecting Jesus Christ.
Scripture is clear when it comes to Hell, and where the seed falls. Not all will be saved, there will be gnashing of teeth. It isn't pretty and its not supposed to be. It isn't a threat, but simply the reality of rejecting God, of which all good comes from. If you choose to stay in the dark, then you do not get the benefits of the light. So if you consider all that is pure, holy, and good about God, to dismiss Him and to be apart from that, what will surround you? Not things of the light.
With such a sad reality, there then comes the Gospel. Not an ultimatum of demand, but of circumstance. Humanity is condemned, but Christ came to save the world and not condemn it. Did He fail? No, salvation is available to all that would believe. That is the caveat. Faith.