That's because no one can come up with a theme for an arcane half-caster that has stuck with the playerbase. There's been countless classes made like that (Duskblade, Swordmage, Bladesinger etc.) but none of them have ever kept any sort of traction with players. My own personal opinion is that it's because there hasn't been a story to the class that people have been inspired by... it's always just been "there's a mechanical hole to fill, let's fill it!". But a mechanical hole without a narrative function in the world makes the class nothing more than a Fighter/Wizard multiclass, just like the Eldritch Knight. And no one needs an entirely new class if the Fighter/Wizard multiclass is the exact same thing within the story of the campaign world.
As farr as subclasses go, I think bladesinger has a lot of traction with players in 5E.
For me I don't particularly want the class being a narrative of its own. I want to do that myself, both with the background and the playstyle/story arc that develops. The class will set some bounds on that, but the story is in the character not the class. That is one thing I don't like about Warlocks, is that the class comes with a built in story all its own, it is a major element and you need to either fit it into the story and campaign or waive it. I think with bladesingers the change to allow any race to do it made them a lot better.
For example I currently have a 4th level Glasya Tiefling Arcane Trickster, named Xane, who grew up essentially as a captive in the Winter Court in the feywild. She escaped to the sword coast and is in a WOTC campaign (Storrm Kings Thunder). Most of her "story" is looking over her shoudler in fear that the Queen of Air and Darkness will come and take her back. Even though nothing in the campaign relates to that at all, she thinks it does and the DM plays along with this.
Xane's story is worked around the haunted one background but the story has nothing at all to do with her race, class or frankly with the campaign. However I managed to work those elements into it - she obviously took the Fey touched feat at 4th, she knows/speaks infernal as a Tiefling trait but she did not use it growing up so her infernal is shaky (kind of like my Arabic IRL). Any time she is reading anything in infernal or speaking in infernal she struggles for words and meaning, she always figures it out this is just flavor; like as a player I will use poor grammar and speak slowly when she is "talking in infernal". On the other hand when she speaks sylvan (which she got from her background) it is flawless and I make it a point to role play it that way. This story plays into how she acts all the time in game. It plays into how she treats prisoners, it plays into her initial reaction if she sees a creature common to the Feywild "Did the queen send you!".
I love the RP on this character but I could really use the same story and behavior regardless of race and class, I would have to change some little things in her background to explain her different skills and initial training at 1st level but I think the basic story would still be doable with any race and class.