Cash doesn't derive its value from being hard to make. It's paper and ink. I can make reproductions of $100 bills with my home printer. The US dollar is backed by people's faith in the government; it holds value because we all agree that it's valuable. I see no evidence that latinum is anything other than another fiat currency.
Now, printing money at home is not legal
, but that's not what this topic is about. It's entirely possible that replicating latinum at home is illegal for Ferengi, and that only the Ferengi government is allowed to issue gold-pressed latinum. That doesn't make it unreplicable.
The original question was "Why
can't latinum be replicated?" The question starts from the baseless assumption that it can't
be replicated - but no character
ever stated that it couldn't be replicated. So I see no reason to assume that it can't be replicated, because there's no evidence
that it can't be replicated. It's all fanon, based on most fans cursory understanding of economics and finance. Just because the Ferengi use it as currency doesn't prove that it can't be replicated. Financial systems don't require currency to be backed by something like gold to function.