Why Does D&D Not Have a Mageblade Class?

Way back in days of yore, the original version of D&D had an odd rule for elves - they advanced both as Fighters and Magic Users, somehow switching between the two at the start of adventures. In BECMI D&D, the Elf class was effectively what would be known as a Fighter/Mage in 1st and 2nd Edition... and, of course, 1st and 2nd edition had multiclass rules allowing demihuman PCs to advance in multiple classes at once - most notably the elven Fighter/Mage.

When the game moved on to 3e, though, the multiclass rules were changed so that a PC would at least start as a member of a single class. And although they could later pick up other classes, there was no equivalent of the classic Fighter/Mage, and so no real way to build the classic Elf of yore (at least not until you qualified for the Elritch Knight prestige class - or until the Duskblade was added very late in the edition). 4e, for its part, mostly got rid of multiclassing entirely, although it did later introduce hybrid classes which brought back that Fighter/Mage concept.

And now 5e has reverted to 3e-like multiclassing. It does, I should note, have an Eldritch Knight subclass for the Fighter, but...

(Oh, and Pathfinder is basically the same as 3e on this, except that it has the Magus in place of the Duskblade.)

What I've been wondering for a while is why WotC didn't introduce that 'missing' Mageblade class right at the start of 3e, thus plugging the gap left by that one tricky classic archetype.

(Indeed, I even wonder if adding that one class might have been enough to remove the need for multiclass rules entirely? It really was that one weird corner case that was left over from the legacy of the game, so adding a new class might have been enough to cover it.)

All that said, if I were now rebuilding D&D, I think I'd be going with a very different class line-up...

• Hero: A non-magical hero that combines the existing Fighter, Barbarian, Monk, Ranger, and Rogue.
• Wizard:: The practitioner of magic. Can be a prepared spellcaster (Wizard), a spontaneous caster (Sorcerer), or a 'channeller' (Warlock) depending on the player's preference.
• Witch Hunter: The Cleric rebuilt to be much more Van Helsing than currently. Forget the religious trappings of the Cleric, though - the character could be a priest like in the Exorcist, but doesn't have to be. Would still have access to magic, but it would be a learned magic rather than the gift of the gods, and certainly wouldn't trawl the Bible for suitable miracles to convert!
• Artificer: Or Alchemist or Mad Scientist, or... This is the character who draws his power from his gear, a la Iron Man.

In each case, the class should have builds available allowing them to dip into some of the lesser powers of other classes, allowing the Paladin to be built as a Hero (for example), but I don't think I would bother with multiclassing as such - the advantage of a class system is strong archetypes; if you want wholesale blending of archetypes, you probably want a point-buy system anyway.

Of course, that's just me. These days I don't really have any interest in building my own game. Much...