As a "grandfather" of this, felt I should chime in - I have an FX set of TX armor. And money, at least in my case, has been the main reason for not upgrading. That said I DID actually just decide after a few troops (I had been inactive for a while) that I needed an upgrade, at least helmet first. So I am the proud owner of a Black ATA helmet for my TX!! (I know I know, this is the "TK" area) But I've also got a "new" used set of AP armor I'm restoring to join the ranks of the TK club.
So money, and a bit of resistance as the club was founded on FX, and while not accurate - the idea that troopers *have* to upgrade seemed a bit forceful. I know that's not the case, and I'm glad we could still be considered active in the FX, it just felt like forcing us "old folks."
I'm happy to upgrade my TX bucket to a more accurate one. I'm also getting a cloth belt and going to do the mods to the butt plate etc. It just took a bit of coaxing from other troopers and the time and $$ really. But I'm happy now that I'm moving forward to a more accurate suit. Even if it isn't as clean and white as the rest of you TK's