Why aren’t there more competitors in the Single Player, Open World, Fantasy, RPG niche?

Because it is hard to make them. They require a lot of assets, a lot of development time, a lot of writing, etc. Bethesda dominates the genre because nobody else wants to take the risk to pay developers to try for something that might be really expensive and bring back little return. And this particular genre is a nightmare for solo and indie developer teams.

Indie and solo developers want to make a game in this genre, but its unrealistic to expect any will be successful. Even I had deslusions of developing my own before I decided to switch to a slightly smaller genre for my own game project. I think all indie and solo developers at one point have had to come to the realization that its not realistic. Its just too much work.

Bethesda’s game engine, Creation Engine, actually helps them in this case, because it is purpose built for this genre. It is significantly easier for them to make another one because they already have most of the systems already in place. Compared to using generalist engines like Unity or Unreal, Creation Engine (I used to know it as NetImmerse) gives a huge leg up on creating that type of game, significantly reducing the time and money investment required.