Okay but the average modder isn't making a total overhaul fantasy mod (to which the main limitation/time consuming thing is remaking the world). Look at the workshop for EU4 and see out of the thousands of mods how many are total overhaul fantasy mods. Heck look at the hoi4 workshop where virtually all total overhaul mods are still on the topic of interwar/20th century. The only PDX GSG that actually seems to have a lot of mods taking place in separate eras/fantasy overhauls is CK3, the game with the most sophisticated 3D models.
No offence to the small mod makers, but the popular mods are more often than not the overhaul mods, and fantasy or otherwise overhaul mods require some kind of art that isn't present in the main game.
I'll go through each of the games:
EU4's popular non UI/localisation mods:
Anbennar - fantasy mod that requires multiple fantasy races
Third Odyssey - alt history that requires bespoke clothing and hairstyles
Imperium Universalis - time shift that requires bespoke clothing and hairstyles
Ante Bellum - again, alt history that requires bespoke clothing and hairstyles
HoI4:
Kaiserreich - alt history that requires bespoke clothing and hairstyles
Old world blues - Fallout mod that needs a complete aesthetic overhaul, including a myriad of mutant portraits
TNO - alt history time shift which requires modern clothing
You can probably work out how much you need to do to make the myriad of other popular overhaul mods for Hoi4, star wars, pax Britannica ect.
CK3: it has 3D portraits, and production of major mods have been slowed considerably by them.
Elder kings - fantasy, requires a complete overhaul to characters
Game of thrones - low fantasy, requires bespoke clothing and hairstyles
Realms in Exile - LotR mod, requires complete overhaul for fantasy races, most of the world is not implied yet.