The formula was sold to a big pharma company that completely botched the third round trial. It's not that harmful side effects were discovered, but due to a bad testing methodology, the results were not nearly as good as they were. The big pharma company recognized the issue, but a revised third round trial would delay the introduction by years, at which time the amount of profits to make from the medicine were considered too low due to patent expiration. So they just dropped it altogether.
It would be too uneconomical for a new company to kickstart the whole approval process again: as soon as the patents expire, other companies would immediately release their generic variant.
End result: millions of potential carriers of the disease won't see the benefit of a medicine that has been shown to work.