I have dabbled in modding actually but only enough to know that I don't have the time or patience to make the big mods that I'd like to see, or that people with thousands of more hours of experience modding these games haven't managed to complete.

For example, no matter how much modding effort you put into combat, it's still only ever going to be classic floaty bethesda combat. No matter how much you try to improve magic, it's never going to become Dragons Dogma or Kingdoms of Amalur, ya know. No matter how many settlement overhaul or custom NPCs I add to fallout, it's still going to feel soulless and pointless to me, and no matter how many tents or frostbite effects you add to skyrim, it won't become as immersive as Outward.

Mods can improve what is already there but in my experience, they can never replace or rework core foundations of games, either because the modders don't have enough time and experience to do it (resulting in janky or unbalanced messes), or because the engine/API doesn't support it.