I personally think the current pre-trib rapture attention (NOT necessarily the doctrine) has to do with the mass-marketing of the Christian religion as a feel-good religion where it's all about what God can do for you and how He can make your life less of a burden. You don't hear persecution preached too often, as is evident by a survey I saw indicating that very few Christians (especially American Christians) are aware that Christians are being martyred at an unprecedented rate in the world. I think the doctrine is being fueled by a sense of escapism among the weak-hearted who don't have a proper understanding of how God could allow His children to endure tribulation.
A note to pre-tribbers: I'm not in any way mounting a challenge to this doctrine scripturally, merely attempting to explain what I feel are the reasons for it's explosive spread recently.