Hi Introspection,
Why would we choose to define ourselves by a label which emphasizes something we 'were', rather than something we are or would like to become?
I don't know about others, and I am fairly new to this ex-jw status myself, having only realized the truth about the 'truth' about a year ago, and having attended meetings (though under duress) semi-regularly up until a few weeks ago.
But, I think a possible reason is that being a JW (in my case, 27 years)is one of life's experiences which marks us in a way that trickles, or in some cases, floods, through our lives ever afterward. Of course, we are all the sum of our past experiences, but having been a witness permeates my soul in a way which kindergarten never did. When I was in school, whatever grade, I knew that it was, by it's nature, a transitory stage. And though I might have used my grade level as an identifier in certain situations, it was never all I was about.
But 'being a JW' is what a JW is all about. It is THE defining characteristic of the faithful JW. Whatever else they may be, married, job status, parent, hobby, ...all are disposable in the face of being one of Jehovah's Witnesses. For the faithful witness, all future hopes and prospects, current relationships and activities are either filtered through or actually defined by the WT world view.
When leaving such an all-encompassing, insular culture, how can one help but be somewhat defined by their WT legacy, or at least occasionally view life from the perspective of an escapee?
Besides, being an 'ex', to me is one way of taking my self back, out of their hands. It means I have made a conscious decision to free myself. It also allows immediate empathetic understanding, with those of similar background, to take place.
On the other hand, I don't proclaim ex-jw status as a beginning fact about myself in general, but seek to redefine myself in new ways which have nothing to do with that.
PS. I have been reading some of the information on the link you sent me. There is a lot to assimilate there, but I will keep working on it.