Then why are there so many songs about rainbows?
I am with you on that. Where are all the songs about identity crises and aspirations and death?
What’s so amazing that keeps us star gazing?
There are genres that do not rely so heavily on love- Gangsta rap, for example.
Sort of the yin & yang of lyrics, eh?
2Pac’s song, Me and my Girlfriend, is an extended metaphor about his gun, in the form of a love song.
I think that love/relationship songs are more a staple of commercial pop and dance music than as lyrical content for more serious or deeper genre-based music. As has been mentioned. love songs are not much a staple of metal (discounting hair bands, which were pop), or gangster rap or several other genres unconcerned with pop success. Love songs are a hackneyed component of pop and dance music because that kind of music makes its money off of melodic hooks, not lyrical content. The lyrics are just sounds to put to the hooks, and love songs are easy and light and don’t step on the hooks.
It depends, and this may be something that has to do with language, I don’t know. But in some genres in other languages, this is not the case. For example in Spanish, Silvio Rodríguez, Mercedes Sosa, Víctor Heredia, León Gieco, and other members of the “nueva canción” style, which usually sings protest songs, have written and recorded some of the best love songs I know. In fact, they blend the political with the romantic, as they describe their partner as someone whose love and companionship leads them to continue in their political struggles (short summary).
What else is the hipster-generation-Y-crowd going to sing about?
Once we hit 40 you should expect slew of songs about divorce, depression, and midlife crises.
Professional songwriters and musicians are rarely also professional historians or scientists. So it’s pretty unusual to come across a song about the battle of Hastings or curved space-time.
But everyone has their heart broken sooner or later.
I suspect that the prevailing attitude in the music industry (at least among execs, managers, and PR & marketing types) is that there’s basically two categories of song subjects: love/sex, and the quirky topics.
The lion’s share of my favorite bands and songs fall in the latter camp.
Shall we start rattling off a few of the quirky-topic specialists? Let’s do, but in a new thread… [to be set up in a moment]
So that song isn’t a metaphor for erectile dysfunction?
No, it’s The Rack of the Edmond Fitzgerald, about the breast implants of a transsexual.
folks dig fucking. me too, i s’pose.
Theres just got to be a song about Haem..Hemah …fuck it piles.
That and weak bladders at night.
Or Sink the Bismark.
Back in the days when Tipper Gore and them wanted violent lyrics censored (parentel advisory labels stuck on rap CDs), Frank Zappa said something along the lines of, “if violent X-rated lyrics are going to incite violence and suicide among the young who listen to them, how come 95% of popular songs are all about love and relationships, and how come we aren’t all walking around in love thinking about our relationships?” Cause and effect. Well, maybe we all ARE as well off as we are because of sappy love songs? 
I don’t pay much attention to lyrics, sappy or not, but if the default is lovelovelove, I’d rather hear that than ‘worship the devil/beat up your ho/jump off a bridge’ when I DO hear the words.
Back in olden days, like with folk songs, there was more variety in lyrics because these songs told stories, like fairy tales or legends. People knew of these stories by listening to popular ballads of the day, that was their entertainment and a way of passing on the stories. Now when I drive the car, an innocuous I-love-you-girl song as background noise suits the purpose, I don’t have to ponder the meaning of The Long Black Veil or who ‘she’ is in She’ll Be Coming 'Round the Mountain When She Comes.
But that’s totally about a relationship.
Because love is all around us, and it will not only keep us alive but lift us up where we belong. Love is all that matters; it’s the answer - it’s not only the greatest thing, it’s also the oldest yet the latest thing. They also say it’s a blessing and a gift. Basically, all you need is love.
(My bolding). I’ve known a few women like that.