Itās not the term that is the problem, itās the soteriological construct (sorry for the jargon - it means theory of salvation) that says that the faithful will not have to undergo the trial/tribulation because Jesus will snatch them up before it happens. It also posits a multi-staged Second-Coming, in which Jesus returns for the faithful and scoops them up, then allows/unleashes all kinds of suffering, then returns in triumph to establish the Kingdom (and then, in some versions, brings about the final end a thousand years later . . .)
But Jesus specifically told His followers to be prepared for the trial, to expect and persevere through persecution. And He never suggested that there would be some āsecretā return. In fact Paul wrote in a different, later letter that the resurrection of the dead and the assumption* of the living faithful would be simultaneous: āin a moment, in the twinkling of an eye, at the last trump: for the trumpet shall sound, and the dead shall be raised incorruptible, and we shall be changed.ā (1 Cor. 15: 52)
*Make no mistake, what Paul is describing here is Assumption, and given the likely date of the writing of 1 Thessalonians, he may well be writing this at least in part in response to the Assumption of the Virgin.
I am puzzled by your question about Purgatory - why would you expect this passage (or, by implication, any passage about the End Times?) to contain references to Purgatory? If you want to see Paulās teaching on Purgatory, read 1 Cor. 3:10-17.