It seems to me this cannot possibly be a hard limit. If it’s a hard limit it’s only because AWS wants to milk you dry.
https://docs.aws.amazon.com/organizations/latest/userguide/o...
Maybe it was quicker to implement with a hard limit, or there is some internal service that can't easily handle large volumes of account removals. But if it was Amazon losing money from this limitation instead of the customer I imagine it would be fixed pretty quickly.