Frozen_Heart
Hero
The core concept and mechanics have always existed, but always in differing and scattered forms. Not only that, but they lack a narrative class story unlike every other class except fighter and wizard. The links to elves formed a potential hook, but one which wasn't sustainable long term due to the issues with linked species and classes.that's the thing though, the swordmage is not just a 'person who hits and magics', they're a person for whom hitting and casting is one and the same, none of the 5e classes properly do this, the combat and magic mechanics are so separate from each other in all of the attempts in 5e that you don't have the fundamental seamless synergy of the two forces that is the foundation of the class concept.
even if it's had different names and executions, the core concept has existed and been strong through DnD's history.
Now that paladin has essentially eaten the spellstrike niche with all its smite spells, this has left the concept in a really poor state. Its signature mechanic got nabbed by another class, while it lacks a proper class story beyond its mechanic.
Eldritch Knight and Bladesinger tried eating some scraps of the narrative niche, but without the mechanics which actually make the concept fun, they feel hollow if you've played a previous edition or pathfinder gish.
But you can't simply add a class which has its entire narrative and mechanical identity be 'hit with weapon and magic damage through weapon'. That's just a paladin minus the entire paladin class story. Adding that would be a serious case of stepping on toes.