People don't like being depressed, but most can identify with being depressed. Therefore, songs about that topic will resonate with most people on some level, and people will listen. If people listen, the song will make money for the singer and producer. Supply and demand dictate that if a certain kind of song makes money, more of that kind of song will be produced.
I haven't tried to do any kind of statistical study, but I don't really believe that songs about depression or lost love make up either the majority or a plurality of songs being produced. Maybe some people notice those songs a little more than the others, but I don't remember them being that prevalent.
Bill
Oh, they love it, alright.
I'm reminded of a short story where an old woman ran across a telephone service. You could dial a number, and it would give you a feeling of a certain emotion. The old woman dials happiness. She's happy. She dials frustration. She's frustrated.
But then, she reaches mild depression. Not intense, but mild depression. She receives it. Then she goes back. And back. And back. She becomes addicted to dialing mild depression.
Things that are kind of depressing are what sell. People LOVE to feel mildly depressed. It sparks an emotional reaction. People like to emotionally react to something; it shows the power of the material if they can react a certain way.