US clinical trial sites5 Sep 2022 08:46
Could be that they were waiting for orphan drug status before they come online. Note the first incentive:
The FDA has authority to grant orphan drug designation to a drug or biological product to prevent, diagnose or treat a rare disease or condition. Orphan drug designation qualifies sponsors for incentives including:
Tax credits for qualified clinical trials
Exemption from user fees
Potential seven years of market exclusivity after approval