Agreed. I think that is something that should never be completely explained - but I wouldn't mind some tantalizing clues on for example what broke the gates originally.
I think the original lore is pretty strict in this regard, with the Omega/Alpha clones I'm not sure how things stand. The "first generation" of capsuleers had to endure rigorous training, both physical and mental, had to be exceptionally smart, physically fit (not have certain hereditary diseases, certain genetic marker making them compatible for the capsule) and many many other variables in a process that at the very least takes 5 years, 7-8 would be more common, which even then would not guarantee success in not wetgraving - and it was so prohibitively expensive that typically most capsuleers were either military or from prestigious government funded institutes - so that is what made them one in a billion, originally.
I assume the new omega-alpha cloning is somekind of evolution to the older technology and today really just about any schmuck can become a capsuleer.
EDIT: I think the oldest player capsuleers are infact 2nd gen capsuleers? There were capsuleers before, but they didn't have the same immortality originally that we did. The Alpha clones are the third generation, if I've understood correctly. Of course this can be theoretically stretched that Jove were the first gen and so on.