All the better songs in Pop culture have a main theme that concerns itself with either love or with death. Both are indeed of the utmost importance.
Only very few songs are really good. Those are the songs our parents like and we like and our children like too. We hum them without further thought as we do the dishes. They get covered in all styles. They resonate in our hearts. Most of these songs that are that good, have this unnamed quality to them. They describe life itself, somehow.