Why is the retracted data still available?

For once published data, we can restrict use of the data if conditions are met.
In case of the use restriction, DDBJ will not include the restricted data in periodical releases and remove from all services of DDBJ.
However, the data is permanently available on getentry if queried by its accession number. This rule is not applied when the data is published by any mistake of INSD. This policy is documented in “Nucleotide Sequence Database Policies” as follows;

All database records submitted to the INSD will remain permanently accessible as part of the scientific record. Corrections of errors and update of the records by authors are welcome and erroneous records may be removed from the next database release, but all will remain permanently accessible by accession number.

In addition, there are third-party databases using INSD data. We can not support to delete data of these databases. If you are to delete the cited data of third-party databases, you have to contact the relevant database.

Reference: INSDC Status Document