Some of these people had jobs, were graduates and had all sorts of privileges.
It's got nothing to do with being poor. More to do with the culture encouraging them to do whatever they want. These people aren't something new, they've always been doing these types of things. Stabbings in schools, burning down people's homes/shops. Nothing new. The only thing that makes it new, is that they realised that they could take it farther than their current circle.
The rest of the country was okay with this mentality. As long as they kept it amongst themselves, amongst the other poor people who have had to endure these people and their activities for generations. That's changed now. Hopefully, more will be done about the mentality that fosters these types of people, and encourages these types of activities, no matter where they might take place in the country.