[Soulsmith] Why do so few people advance to Highgold?

I've just finished Soulsmith, but there's an aspect of Cradle's world I can't quite understand; why are most people stuck at Lowgold?

Assuming Eithan is telling the truth, only 1% of people get to Highgold (and 1% from thereon etc). But I can't really square this with the fact that Lowgold is seemingly the baseline standard of (almost) all humans on the planet. It's not like only a certain section of the population practice SA, everyone does it. Couple that with the fact that most people seem to be Lowgold by the time they're 18 or so & it doesn't make sense to me that so few people advance any further.

This is sort of tied in to how I understand the economy to operate (maybe this changes in later books). At least so far, nobody is really an independent actor; they're all members of a clan or sect - the economy seems to be run by a handful of pyramidal organisations. Everyone does the job their elder or their mum tells them to. There are no individuals or small families (<50 people) who run their own shops or farm or whatever.

So if you're 18, you've got your whole life ahead of you, at least 50 years on average. And people don't seem to suddenly develop an aversion to fighting & cycling, because everyone is seemingly spoiling for a fight at the drop of a hat, and it seems unlikely to me that they'd stop doing their breathing techniques once they reach adulthood. Even if not everyone makes it to Highgold by their early 20s, like Jai Long (who seems to be much more talented than average) surely over the course of a person's life they would eventually reach Highgold by dint of long effort, even if they don't develop as quickly as someone like Jai Long.

Even if it were insanely risky to reach Highgold, so some people are put off, this seems like a world where people (and the people who lord over you) care way more about strength than your life.

1 in 100 people reaching the step just above the baseline seems like an incredibly small number to me. At 30%, I'd have an easier time accepting it. But maybe it'll make sense once I've actually learned how it's done.