To be exact, the hard limit is: you cannot delete more than 10% of your organization's accounts (capped at 200) via AWS Organization within a 30 day rolling window. You can always delete an account by going into it as the root user.
If that was the concern then surely they could enable support to restore accounts during some grace period. The machinery for that already exists for people who completely close their AWS accounts down.
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.
