A lot of times different ways that people act are different ways of getting emotional needs, even if that isn't a conscious choice. In this case it is likely that they want recognition and sympathy for different pains they have have. Or, it's more likely the case that the different hurts they have (being lonely, being picked on, getting hand-me-downs, whatever) are easily brought to mind. But when the person tells someone else about the things in their life that bother them, it's possible that someone could say "hey, it sounds like you are really lonely being an only child" and they would feel better.

Some different example needs are things like attention, control, acceptance, trust, play, meaning. There is a psychological model of how humans work that thinks of emotional needs similar to physical needs like hunger, etc. So people have some need for attention, and will do different things for attention. They also have a need for emotional safety, just like physical safety. So just like if someone was sitting on an uncomfortable chair will move and complain about how their chair is uncomfortable, someone will do a similar thing if their big brother is picking on them.

Another reason people often make it look like they are being oppressed is that they feel oppressed. I don't know if you are mostly talking about people your age, or everyone, but it is not a surprise to me that lots of kids feel oppressed, since school and their parents prevent them from doing what they want. Plenty of adults express similar feelings though, i just expect not as many.