My assumption: nobody cared anymore, so the owner lost interest in this alt-account.

Note that someone tried really hard to hit 3 million

Oh wow, that's interesting!  I don't recall that discussion about the Merit Cycling Club whatsoever, and though I haven't scanned through that entire thread yet, I don't believe I posted in it. [...] I now know why I missed LoyceV's thread--I have that section on ignore.  Fortunately the thread is still running for some reason, so I'm going to un-ignore it and see about posting in it ASAP.  Thanks for linking to it, OP.

It is very strange that the actual 3,000,000th member registered on this forum would have that name, no?  I suspect that's not a coincidence at all but was done by Theymos or someone who has influence with him.  It could just be someone who was watching closely and had damn good timing, but somehow I doubt that.