Some of the built-in thematic elements of certain races sucks. There I said it. It's pigeon-holed and type-cast so far into a corner that including the race forces you to include the racial elements. I mean I've resolved the thematic issues by completely refluffing the races, but that's a massive PITA.
EX: I wanted to include dark elves but I didn't want traditional "dark fae" and I didn't want Drow, so I had to completely re-invent the wheel. I ended up with a South-American styled "jungle elf". It was nothing like the Drow so the thematic elements were completely thrown out the window anyway.
It seems like you are working extra hard to avoid something that is rather minor.
Or: I resolved to include Dwarves for a change, but instead of them being mountain-dwelling folks I made the island dwelling folks, something akin to a cross between pygmies and Jamacians. So...thematic elements? What thematic elements! I threw them right out the window.
Again, that is more work, than it is worth. Why not just allow the race? I have an entire island chain in my world run by Duegar. Goblins inhabit the islands, but the Gray Dwarves rule from the bowels of the volcano that makes up the island chain. Additionally, I added Kou-tao that fight over control of the goblin villages with the Duegar. My players could pick any of those races if they wanted. It might be a problem if someone chooses a Duegar and another chooses a Kou-tao, so I make make limitations, but outlaw it because I dislike the thematic elements? PAH!!
And: When I do include gnomes, they're more traditional fae, where everything is a joke and the punchline to a joke is someone dies.
If seems like you are rather stereotypical here. Why can't a gnome just be a short trader with a long nose that enjoys tinkering?
Yes, I could have included stock Drow and stock dwarves and stock gnomes, with stock thematic flavor, but honestly when I sit down with players and they tell me they want to play a stocky, grumpy drunk with a napoelon complex and a love for rocks with a bad foreign accent I ask them: why can't you be all that and be a human? Why does that have to be a dwarf? And the answer is simply that they hadn't stopped to consider it.
Because they simply want to be different, and the story element can be fun. Sure they could play a "stocky, grumpy drunk [human] with a napoelon complex and a love for rocks with a bad foreign accent," but where is the fun or the story in that? Its just another human living life amongst other humans, instead of someone different learning to endure life in the human world.
Dragonborn thematic flavor? Ancient race from god-knows-where? It sucks.
Not really, it a story-telling component. That gives the player something "fantastic" to role-play.
Tiefling thematic flavor? The world hates you. It sucks.
Again, its a component that gives the player something interesting and different from real lift to tell an interesting story.
Half-orc soft-rape baby flavor? It sucks.
Stereotype much?? I played a half-orc who's parent fell in love, and the mother chose to live with the tribe till my character's father was killed over a fight for power of the tribe. The mother moved home and was persecuted for her love of someone different. My character shared in that persecution because he was different. Still because he loved his mother and because it was her home, he cared for the city even though no one there really liked him. It was a story-telling component that made the character interesting, and made for great roleplaying.
The forced Greyhawk flavor in 5e? It double-sucks.
I disagree that it sucks. Gygax did a great job with Greyhawk, its just not my kind of world. The feel is spot on with the original vision of D&D, which is what has really draw players to the game.
The flavor in 5E sucks if you want to step outside the Forgotten Realms for more than 5 minutes. If someone wants to play the thematic flavor straight from the book, I'll flat out tell them they're at the wrong table.
Seems to me you simply aren't interested in the roleplaying beyond your ideal bubble.
The thing is we live as humans every day, the point of "Fantasy Roleplaying" is to bring some fantasy into your world. That is why other races exist to allow the player to be something they aren't...at least for a little while.