The problem seems to be that even the line fit (at A or B) approved standard seats are in short supply. So while you have dozens of completely built and outfitted aircraft (like the Hainan B789 and Aeroflot A359) standing around looking for owners/approvals the airlines taking delivery of newly built aircraft are not able to get their seats installed as line fit due to regulatory and supply chain issues. 🤦‍♂️