We don't need them. Some people want them. There's a difference.
I think it's the artists themselves who have decided everybody needs to hear about their recent break-up or their new crush. I know when i wrote on that subject matter it was because I thought those feelings were IMPORTANT. It took me a few years to realize that heterosexual romantic love is actually the world's stupidest, most inane and boring subject for songwriting.
It's not like it's just human nature to endlessly whine about your love life in rhyming couplets. First Nations songs (for example) are actually ABOUT stuff. "The salmon are running, come to the feast." or "Hello, grizzly bear, nice to see you, please don't eat me today" and such like. They're not just banging on and on endlessly about their last relationship like white people. They wrote songs like grown-ups.
If people want to tackle more interesting subject matter, and there is an appetite for it, good for them, IMO.
To this day, my most famous (infamous?) song is a completely twisted gospel parody called "Bend Me Over, Jesus (and Give Me All Your Love)". It's a song I've only sung in public like two times (out of hundreds of shows), and also the first (or only) song people remember if they were at one of those two shows.
Another one that goes over well is a perky song about the up side of Armageddon. By the end, people are usually laughing and singing along. Or appalled. Same reaction for Bend Me Over Jesus, now that I think of it.
My point is, I've written about 70 songs, and nearly ALL the ones people remember and love are NOT the ones that are about how I personally feel and how my relationships are going.
So I don't think this irritating heterosexual love song radio saturation is a demand-side problem.