I had an Insight a while back about generic/patchwork settings – specifically Golarion, but it also applies to some degree to Forgotten Realms and Greyhawk. These settings are designed so that whatever adventure you come up with, as long as it fits within a certain core D&D-ness, you can find a place for that in the setting. Gothic Hammer Horror stuff? That's in Ustalav. Travel through jungles to explore ancient ruins? Mwangi's down there. Pirates? My man, let me introduce you to the Shackles. Genies and deserts and stuff? Have you ever been to Katapesh?
This works well for Paizo's goals, because their primary thing is making adventures. The whole point of making Pathfinder in the first place was "We're good at adventures, but the game we're making adventures for is out of print and we care neither for the successor's rules nor the terms under which we can support it, so we're making a clone of the game so we can keep making adventures."
A more distinctive setting probably doesn't support all that stuff, but it is instead better at providing things that make you go "That's awesome, I want to do something with that." Dino-riding halflings robbing the train on the lightning rail? Warforged being exploited as a tireless workforce, creating tensions with meatbags? Cyran refugees exposed to bigotry, and some responding by trying to carve out a new kingdom for themselves? Spy/diplomat intrigue in the divided city of Thronehold? Murder on the Orien Express? Fighting aberrations side by side with noble orc heroes? A church ruling a country and needing to balance its holy mission with the often dirty business of governing? Those are all cool ideas that jump out at me when I read the Eberron books, and don't really work in other settings.
In other words, kitchen sinks are for "I have a neat idea, and here's a place where I can do it" while distinctive settings are for "Here's a cool thing, that gives me a neat idea."
