People want to be popular. It is possible to achieve people liking eachother more overall. But there is indeed a kind of scarcity in the sense that even if some fully likes and even loves everything about you, there is a limit to how much loving attention and time they can offer. So if that person fully loves two people, the attention you get is cut in half. Hence, jealousy.
I thought only teenagers wanted to be popular.
But it's true we crave attention. We're all attention whores. Attention is the fundamental currency of human relationships. We give it hoping we'll get some back. That's how it works.