From what I can read from Barbarian is saying (and it agrees with what I have seen in the various communities I've worked in with significant poverty), EVERYONE is making choices within the range of what's possible for them, in their situation.
Sadly, in some circumstances getting married at 12 or 13 is a more attractive choice than remaining unmarried.
If you have the choice between a 'blesser', as they're called here in South African poor urban communities (older man who gives you mmoney/clothes/food etc in return for sex), or dropping out of school through lack of what he provides, which do you choose?
OF COURSE no-one should have to make that choice. OF COURSE they are being exploited.
But you might decide (as many girls do) to have the 'blesser' and continue with your education - and to have your own boyfriend of your own choice in parallel. Because without an education you have no chance of ever being in a position to be financially independent enough to leave behind being exploited.
And not all men are in a position to make independent choices either. Be humiliated, an outcast, possibly be beaten and/or raped because you are assumed to be homosexual? Or agree to marry the 12 year old and have sex with her just as all your friends and family do?
The age of consent here is 18 - it's also one of the worst countries in the world when it comes to child rape.
The majority of the world's population live in situations where their choices are extremely limited, and mostly involve trying to survive as best they can - what is the least worst option?
If you really want to do something about it, support organisations that work with locally based partners to educate, challenge from within, and provide genuine choices and alternatives (and those that pick up the pieces).