Hello samuel23,
Question: Why would Jesus tell Peter, James, John, and Andrew, that He would return AFTER the great tribulation to gather the chosen?
First of all, you have to understand that the gathering of the church vs. the Lord's return to the earth to end the age, are two separate events. Until you understand this, your end-time conclusions will all be in error.
Once the church has been completed, the Lord will descend from heaven and the dead in Christ will rise first. Then those believers who are alive at that time will be transformed into those immortal and glorified bodies, with the whole group meeting the Lord in the air where he will take us back to the Father's house.
At the gathering of the church Jesus does not return to the earth, he only comes to resurrect the dead and change the living where takes the entire group to the Father's house in heaven.
In opposition, after God's wrath has been completed, at the end of that seven years, the Lord will return to the earth to end the age. In addition, when He returns at that time, those who will have previously been resurrected and the living who were changed, will be following the Lord out of heaven to the earth riding on white horses - Rev.17:14, 19:14
Gathering of the church = Jesus meets us in the air and removes believers from the earth
Second Coming = Jesus returns to the earth to end the age and the church returns with the Lord to the earth
Another important factor that you are not understanding is that, there will be other groups on the earth after the church has been gathered. There will be the 144,000 from twelve tribes of Israel, the woman of Rev.12 (unbelieving Israel) and the great tribulation saints, who are said to be from every tribe, nation, people and language, which makes them all Gentiles. These groups are not the church, but will be here during the time of God's wrath, during that last seven years.
To answer your question, when Jesus told Peter, James, John and Andrew that he would return after the great tribulation, he was speaking of his return to the earth and was not referring to the gathering of the church. The on-going problem is that, people merge these two events together as being the same event, which causes their error in properly interpreting end-time events.
What return of Christ to gather the believers did the church believe in BEFORE Paul was converted and wrote the Thess letters(there was only the return described by Jesus).
In Paul's letter to the Corinthians, he reveals the gathering of the church as a mystery (1 Cor.15:52), where the Lord's return was not a mystery, for they were all aware of that teaching. Paul through direct revelation from the Lord received the information regarding the event of the living being transformed and being caught up at the time immediately following the resurrection. Regarding this, Paul did not say that the Lord was returning to the earth at this event, but coming to gather the church and to change the living and that we would meet him in the air.
Both John 14:1-3 & 1 Thes.4:13-17 has the Lord coming to get the church and taking them back to heaven. Whereas Matt.24:30-31, Jude 14 & Rev.17:14, 19:11-21 has the Lord returning to the earth and the church with him.