How is it that some money mules never get caught? a money mule is someone who reships?

goods from an "employer" for anyone who doesnt know what they do...... money mules in first world countries eventually get caught but what about the ones that are living in third world countries? why is it that these types of scams are fully decomissioned once and for all globally? can a money mule not receive money if his/her "employer" gets caught like in nigeria? can someone please tell me if these people can keep doing this forever or just for a while? i.e. money laundering........