From the beginning of PoE1's development, I got the feeling that the clear prority for the game was to nail down the IP (both with a setting different enough to comply with legal requirements but at the same time familiar enough for IE players, and with a new rule-system) in the hope that it would become successful enough for Obsidian to milk it to death by licencing it (or even to sell the company, who knows). As opposed to, let's say, focus on plot, interactions, encounter design, writing, etc. etc.
If this were true, then Obsidian didn't even need to bother with creating a setting that was clearly differentiated. After Gary Gygax was forced out of TSR at the end of 1985, the Forgotten Realms setting was created as a replacement for Greyhawk, and it was intentionally designed to be as bland and generic as possible to appeal to the lowest common denominator seeking a history-less and culture-less pseudo-medieval setting for their AD&D campaigns. All Obsidian had to do was to manufacture their own pseudo-medieval Europe, ultra-generic collection of city-states, leave out whatever D&D monsters are still under copyright by WotC/Hasbro, replace
hobbits halflings with a different race, and substitute their own pantheon of deities. All of that saved effort could have been spent on other aspects of the game.