I mean there are 3 people (as far as they know) with this specific mutation. Time, money, and capable scientists are limited. Allocating these resources efficiently means that the more rare disease don't get as much attention, but this also means that you're saving more people. Just not those with the rare conditions.
From the article
> The rare label is wrong and limits progress. These are not rare. These are genetic and have the same root cause. We need a systematic, platform-driven approach to fix these typos. We need a spell check.
Yes, there are millions with some mutation. But changing around mutations needs to go through some form of medical process to see if it's safe. The current processes are there because historically there has been a lot of abuse for profit. We can't just platform allow any genetic editing. Some of these edits might be dangerous.