Its unfortunately extremely common for customers and enterprises operating in AWS to have chosen a workload/storage bearing account (more than likely, the main production account) as the Organization Management Account (formerly known Organization "Master" account, before AWS adopted better naming).
Many customers and companies operating in AWS made this decision in 2018 or so and its unforunately not something that can be easily changes as of today (2024). Many customers have requests to AWS to make a friendly path for rehoming the Org Management account but last I heard it is still not prioritized. Thus, we as customers are left to go through the nerve-wracking, if not dangerous process of migrating to a new AWS Organization in order to align with modern best practices and reduce common privilege escalation and account to account lateral movement concerns (made worse if you happen to have enabled things like Cloudformation Stacksets, Control Tower, or other powerful services in the s