>>15673185TES began as a game based on the DND games run in the office. They were working on something else (a gladiatorial arena game based on different gladiatorial teams fighting) but decided they were more interested in their DND campaign so made the game about that instead. This is very visible in their first 2 games which were very generic. The 3rd game (and redguard as well) was the 1st one to get away from that, actually feeling like a much more fleshed out world while still being understandable and believable.
As it takes places in Morrowind, it has the big evil volcano there as an important part, which was established already in their earlier games. Dagoth Ur was the pen-ultimate dungeon already in Arena.
The reason Oblivion became so generic is because Todd Howard watched the LoTR movies.