When did we decide that love isn't serious?

One of the biggest criticisms hurled against books for girls/women is that "they're just about romance". As if romance (and by extension, love) is just a frothy, insubstantial, silly thing that isn't worthy of discussion or exploration. Love affects every single person on the planet, more personally and profoundly than war or catching big whales or dead girls in country towns. And it doesn't just happen to girls. Boys fall in love too. We all do. It's part of our evolutionary reason for being.  It's inspired poetry (good and bad, mostly bad) and music and art. So how come it isn't "literary"?

Here's Stephen Fry from his book The Liar.

It had taken him two painful terms to identify the symptoms. He looked them up in all the major textbooks. There was no doubt about it. All the authorities concurred : Shakespeare, Tennyson, Ovid, Keats, Georgette Heyer, Milton, they were of one opinion. It was love. The Big One.

Cartwright of the sapphire eyes and golden hair, Cartwright of the Limbs and Lips : he was Petrarch's Laura, Milton's Lycidas, Catullus's Lesbia, Tennyson's Hallam, Shakespeare's fair boy and dark lady, the moon's Endymion. Cartwright was Garbo's salary, the National Gallery, he was cellophane : he was the tender trap, the blank unholy surprise of it all and the bright golden haze on the meadow : he was honey-honey, sugar-sugar, chirpy chirpy cheep-cheep and his baby-love : the voice of the turtle could be heard in the land, there were angels dining at the Ritz and a nightingale sang in Berkeley Square.

Does that sound soppy? Why? We all go there, whether it's requited or not. Even educated fleas do it, apparently. So how come when we write about it, it's not "real" literature? Not unless it's ALSO about the Thatcher era, or your alcoholic mother and absent father, or dead girls in country towns? Patty Smyth pointed out that Sometimes Love Just Aint Enough, but I want to know why?