Any “millennials” beating down the door to join those “churches”
...plenty of these millennials are joining the mega churches, where worship consists of having song and fun, and ‘preaching’ is meant to be ‘interpretive’...
...by the way, all denominational churches, in addition to the ones you named, are suffering from this poaching...
A lot of megachurches (as well as televangelists) ARE denominational as well. For example, Saddleback Church is SBC, LifeChurch.TV is Evangelical Covenant, Church of the Resurrection is United Methodist, etc.
As for me, I fail to see the appeal of both megachurches and non-denominational Christianity. I wouldn't want a "pastor" who you can never see face to face because he ministers to 20,000 other people on Sunday, nor would I want generic "non-denominational" sermons whose only theology is that they "follow Jesus" but don't discuss specifics like the Holy Trinity or virgin birth.
Some non-denominational "MegaChurch" may have 20,000 members, but hardly beats a organized Christian church that has millions or billions of members.