There are many countries that refuse to take back their citizens (despite the international law). In that case you either need to kep them detained in your cou

There are many countries that refuse to take back their citizens (despite the international law). In that case you either need to kep them detained in your country with the problem of space, protests, haggling with the recipient country; or outsourcing the problem, possibly ultimately cheaper. We have the problem in France: convicts are not accepted by their country. Being a lawful country we are basically stuck.