The definition of the Rapture is simply this: God's people will rise in the air to meet Jesus in the clouds upon His return for those who have received Him as their savior. The 'saved' who have died will precede the living in this event. First, the dead who received Jesus while living will rise and then the living will all ascend to meet Jesus in the air.

There are many scriptures that address this event. The following is from
1st Thessalonians, chapter 4, verse 15:
¹⁵I can tell you this directly from the Lord: We who are still living when the Lord returns will not rise to meet him ahead of those who are in their graves. ¹⁶For the Lord himself will come down from heaven with a commanding shout, with the call of the archangel, and with the trumpet call of God. First, all the Christians who have died will rise from their graves. ¹⁷Then, together with them, we who are still alive and remain on the earth will be caught up in the clouds to meet the Lord in the air and remain with him forever.

There are highly regarded even famous preachers who teach a false doctrine. The false doctrine that the church will be raptured before The Great Tribulation.

I have no doubt the Rapture is fact. My question is why are "they" misleading the people as to when the rapture occurs?

The theory that the Rapture occurs BEFORE The Great tribulation is in direct conflict with Jesus' teaching. Why do these teachers teach a false doctrine?

I do not like to just give you scripture to read but this says it better than I can...

Read it for yourself, Matthew chapter 24:

³Later, Jesus sat on the slopes of the Mount of Olives. His disciples came to him privately and asked, "When will all this take place? And will there be any sign ahead of time to signal your return and the end of the world?" ⁴Jesus told them, "Don't let anyone mislead you. ⁵For many will come in my name, saying, `I am the Messiah.' They will lead many astray. ⁶And wars will break out near and far, but don't panic. Yes, these things must come, but the end won't follow immediately. ⁷The nations and kingdoms will proclaim war against each other, and there will be famines and earthquakes in many parts of the world. ⁸But all this will be only the beginning of the horrors to come.

    ⁹"Then you will be arrested, persecuted, and killed. You will be hated all over the world because of your allegiance to me. ¹⁰And many will turn away from me and betray and hate each other. ¹¹And many false prophets will appear and will lead many people astray. ¹²Sin will be rampant everywhere, and the love of many will grow cold. ¹³But those who endure to the end will be saved. ¹⁴And the Good News about the Kingdom will be preached throughout the whole world, so that all nations will hear it; and then, finally, the end will come.

    ¹⁵"The time will come when you will see what Daniel the prophet spoke about: the sacrilegious object that causes desecration standing in the Holy Place" reader, pay attention! ¹⁶"Then those in Judea must flee to the hills. ¹⁷A person outside the house must not go inside to pack. ¹⁸A person in the field must not return even to get a coat. ¹⁹How terrible it will be for pregnant women and for mothers nursing their babies in those days. ²⁰And pray that your flight will not be in winter or on the Sabbath. ²¹For that will be a time of greater horror than anything the world has ever seen or will ever see again. ²²In fact, unless that time of calamity is shortened, the entire human race will be destroyed. But it will be shortened for the sake of God's chosen ones. ²³"Then if anyone tells you, `Look, here is the Messiah,' or `There he is,' don't pay any attention. ²⁴For false messiahs and false prophets will rise up and perform great miraculous signs and wonders so as to deceive, if possible, even God's chosen ones. ²⁵See, I have warned you. ²⁶"So if someone tells you, `Look, the Messiah is out in the desert,' don't bother to go and look. Or, `Look, he is hiding here,' don't believe it! ²⁷For as the lightning lights up the entire sky, so it will be when the Son of Man comes. ²⁸Just as the gathering of vultures shows there is a carcass nearby, so these signs indicate that the end is near.

    ²⁹"Immediately after those horrible days end, the sun will be darkened, the moon will not give light, the stars will fall from the sky,and the powers of heaven will be shaken. ³⁰And then at last, the sign of the coming of the Son of Man will appear in the heavens, and there will be deep mourning among all the nations of the earth. And they will see the Son of Man arrive on the clouds of heaven with power and great glory. ³¹And he will send forth his angels with the sound of a mighty trumpet blast, and they will gather together his chosen ones from the farthest ends of the earth and heaven.

See? He comes after the Persecution, The Great Tribulation, Those Horrible Days.

Let me repeat the scripture - spoken by Jesus, the SON OF G-D...
²⁹"Immediately after those horrible days end, the sun will be darkened, the moon will not give light, the stars will fall from the sky,and the powers of heaven will be shaken. ³⁰And then at last, the sign of the coming of the Son of Man will appear in the heavens, and there will be deep mourning among all the nations of the earth. And they will see the Son of Man arrive on the clouds of heaven with power and great glory.

I rest my case!
Now ask yourself why "they" preach a false doctrine. "They" are not ignorant. Don't you be ignorant either! Do not buy into their false doctrine and leave yourself or your family unprepared. Prepare for tough times and prepare your loved ones for tough times if you are living in those last days. This way you won't be dissappointed in the teachings of the bible.