Why are Christians divided when it comes to the rapture ?

Christians throughout all of Christendom are divided on almost everything in the Bible, that is why there are so many denominations, and then you have the ones claiming to be nondenominational, but for the most part they all cling to one false teaching, that of the trinity. Then you have the Catholics claiming to be the one true church yet they are divided as well, Roman Catholic, Eastern Orthodox, etc. There is one Christian Congregation that throughout the entire inhabited earth believe the same thing, teaches the same thing, and are of one mind in God's word. They live according to God's word and follow closely in Jesus Christ's footsteps. And just as the Bible teaches that there are many parts of the body, even though they are many individual congregations in all the nations they are all in union together as one congregation of God, one brotherhood of Jesus Christ's disciples, one brotherhood of worshippers of Jehovah God. 

There is disagreement about the rapture because many churches do not teach about it, and many Christians are lazy about studying about it. Plus, nobody enjoys thinking about leaving their unsaved loved one's behind. 

Only spiritual dimwits believe in that claptrap. It's not biblical in the least. 

I do not mean to offend anyone but, where do you people get that 2nd coming of Jesus?  When was his first arrival?  OK, whenever that was, but the story is that he was crucified (I do not believe that) when? about 30CE or a few years before?  So he was dead perhaps by 33 or so CE.  Then how did he show up in Jerusalem in 70CE?   That story is twisted and made up to look mysterious to those who believe it. There was no Jesus, and the NT is not telling the true story.

Cause none of them read the bible they just listen to pastor pork chop on sundays

For the same reason Protestants are divided on everything else - the arrogance of one Catholic priest who thought He could do a better job of interpreting the Bible than the Church Jesus Christ founded, to which He promised the fullness of God's truth, which compiled the Bible under the guidance of the Holy Spirit. Before Luther died there were already half a dozen other Protestant denominations that had rejected his denomination because they disagreed with his interpretations of the Bible. Today there are over 6,000 Protestant denominations, each claiming to follow "the Bible alone", yet the beliefs/teachings of each denomination contradicting the beliefs/teachings of the others. Truth cannot contradict truth, so obviously untruth is rampant in this unbiblical manmade tradition. Which is why the clearly stated will of Jesus Christ concerning His followers was and still is "That they all may be ONE, even as I and My heavenly Father are ONE". Which is why the one Church He founded remains one in belief, one in teaching, one in worship, one in biblical understanding throughout the world after 2,000 years with no denominations.

It's not actually belief in Christians alive at the time of Christ's appearing being taken up to meet Him in the air that is the problem. It's a comparatively new, associated teaching as to WHEN this should happen that causes the division. No Christian should disagree with 1 Thess. 4:13-18. A time will come when dead Christian corpses will arise from their graves, being transformed by resurrection, to meet Christ in the air, then those Christians still alive at this time will be caught up ('raptured') to join them in the air. That is a biblical teaching. The problem is with a new teaching in the 1800s about a Futurist, Premillennial, and Dispensational interpretation of scripture. THAT is what causes the division! There never was any such division prior J.N. Darby and his disciple W. Kelly who began to teach a ‘secret’ rapture which they conceded could not be found anywhere in Revelation ch. 4.

In 1830, in Port Glasgow, Scotland, fifteen-year-old Margaret MacDonald attended a healing service, where she was said to have seen a vision of a two-stage return of Jesus Christ. The story of her vision was adopted and amplified by John Nelson Darby, a British evangelical preacher and founder of the Plymouth Brethren.

He taught that Christ's return would be a secret event. He identified the ecclesia, assembly, or church, with the 24 elders seen in heaven in Rev. 4:4, requiring us to assume that somewhere between the end of ch. 3 and the 4th verse of ch. 4, a rapture involving the Lord’s return and the glorified resurrection of the bodies of myriads of saints, raised from earth to heaven in unapproachable light, was so secret that John missed it. Kelly claims, ‘This most solemn and blessed event must occur therefore between chapters 3 and 4 of this book.’ Then why did John totally omit even so much as the briefest hint to ‘this most solemn and blessed event’? John wrote not a word, nothing. But Kelly insists against John’s deafening silence as to this ‘most solemn and blessed event’ that it ‘must occur’ to suit his preconceived premillennial prejudices - John missed it.

It is Darby's dispensationalism, with its divisions of history and its two-stage future return of Christ, that caused division among Christians where, before, there was none.

There's basically an extremist fundamentalist fringe of a few people, mainly living in the States, who believe that.  Nobody else.

Oh, come on.  It didn't exist till Darby made it up in 1830.  Why would ANYBODY believe in it.

That is the way of “opinion”, which the concept of a rapture is, people are free to have various thoughts on it.