I believe the reason it is skipped is because the next restore step MAY include the steps that the undo phase would have undone. If you use NORECOVERY, SQL is expecting another backup file to be included in the backup set. For example, if you restored from 1 full backup and 6 transaction log backups, you wouldn't want it to be "recovered" after the full backup or you wouldn't be able to apply the transaction log backups.
If you use NORECOVERY, the database is not in a useable format until you restore with recovery.
The above is all just my opinion on what you should do.
As with all advice you find on a random internet forum - you shouldn't blindly follow it. Always test on a test server to see if there is negative side effects before making changes to live!