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.
I think part of the problem is similar to that of a ranger and paladin. The ranger and paladin has jobs. The arcane halfcaser would have to have a role in society as well.
The issue is many people don't want to roleplay the occupations of the "advanced classes"
If you are not playing a Ranger in the party why wouldn't he be?
Sure other players can solve those problems and at 11th level they can do it through a bunch of different spells. But barring feats and backgrounds if your party of 11th level cleric, Paladin, Wizard and Rogue go exploring the jungles of Chult, they should have to deal with many of the same problems a 1st level party would. And if the cleric does not have survival and no one else has a decent wisdom it is going to be pretty difficult without spells, much more difficult than it would be with a first level Ranger.
At level 11, between the cleric, paladin, and wizard and your piles of gold, you shouldn't be worried about level 1 exploration threat.
At level 11, you should be dealing with level 11 exploration threats like hurricane, voidstorms, random dinosaur packs, and paraelemental difficult terrain.