Direct message and friends lost in account merge

There is not currently a "merge" operation for accounts, only delete.

When a user account is deleted, their authorship attribution can be moved to another account, but friend/follower lists and private messages not moved as the operation is "delete" and the assumption is that the account owners are not the same and this more personal information should not be reattributed.

If there was a merge operation, I would expect it to work as you expect.

Yes that's the process I am referring to. Why are messages not moved over?

Because it is a user delete operation and there is no assumption that the physical owner of the deleted account is the same as the account taking over the deleted account's content attribution.

The reattribution of content is to allow the content to still be publicly visible even when an account must be deleted. The purpose is not to merge accounts held by the same physical owner.

Adding support for account merging is a valid feature request, but it would be an unexpected behavior for a delete operation and a potential security vulnerability (private messages are otherwise private).