This topic is very disingenuous just based on the notion of looking at it like a "failure". Mods are used and created for personal preference. So unless any video game will allow you to do anything with it, literally anything, mods will always be a thing. Don't like the way a spell looks? Mod it. Don't like the fact graphics may look a little more realistic and prefer a cartoon look to it? Mod it. Want Macho Man to fly around yelling signature quotes? Mod it.

That's not to say that improvements shouldn't happen, but the argument being made by OP is that the very presence of 3rd party tools is a failure of the game. That's just simply not true.