Can't speak directly to their trendiness, as I very rarely see snyone in them IRL, but culottes are an odd bird, to me. Pants that need to be styled like a midi skirt, hmm. Also, I still think of them as a summer-only item, like capris, which limits their versatility. In a mild climate they could work year round, but the silhouette (for me at least) screams summer time. Heavier fabrications just look off to me.