If someone doesn't have a family member or friend living there, there is nothing for visitors/outsiders in those places. No reason to go there. Even if you have family/friends there, they can go to the safer areas and meet you there than you go to the rougher area to see them.
I agree with the other posters though, it's quite sobering to see how other people are managing to live. When I start to bitch that I'm having a rough evening as I've run out of parmesan I know it's time for a trip to the barrio to bring me back down to earth. I have nothing but respect for those people, they got dealt a very different set of cards to most of us on here and they are get trying to get by and get up the ladder.