Imagine you are in jail for life in Russia. Maybe you were falsely accused or maybe you did it. Either way the Wagner group have offered you 6 months at the front line and if you alive at the end you will be free. Would you do it? They are also recruiting from other countries like the Central African Republic.
https://uk.news.yahoo.com/zambian-student-recruited-russian-prison-145912416.html
https://news.yahoo.com/russia-wagner-group-recruits-convicts-213100691.html