Background is always relevant to crime. There are usually aspects of a person's upbringing that point to why a crime has been committed. As I wrote above, these guys are from a country and culture where sexual abuse including against minors is, by all accounts, quite normalized compared to here. They've also grown up in a very violent and unstable environment.
If someone from an English council estate who'd experienced sexual abuse as a child then committed a similar crime as an adult, obviously their background would be relevant.