1. I'm not poor. I don't struggle to live. I'm a teen.
2. "Every human being desires happiness, but only a few of us are rich. So either a basic human need can only be satisfied by extraordinary circumstances, or like our other needs, it must be within every person's reach."
I took this from a book, just in case someone cares about copyright.
Happiness is a basic human need. We all want it. Compare it to other human needs, like health. Everyone wants to be healthy. But given that we're all humans, there are objective laws about how to define and how to maintain good health. Similarly happiness has to have rules and limits for gaining and keeping it.
If happiness only came from money and pleasures, then all you would have to do is satisfy yourself and you'd be happy, as you described in your comment. For that matter, animals would be happy too, because they're always trying to satisfy themselves. But even when we're satisfied we still feel the desire to be happy. We can distract ourselves with other things, but it doesn't work for long.
Try this. Sit in a quiet room for five minutes without worldly distractions. No screens, no music, no books, etc. How do you feel?
3. If you want to talk about what they lack, I will do my best to tell you. Just let me know. It might get a bit religious though. I have a reason for this.