I was talking to another freelancer recently. She was populating a settlement in something she's writing and was asking how two unusual ancestries might interact with each other. I didn't know, but I saw a larger issue and asked how many of the NPCs were human. She said not many, because there are so many interesting ancestries available, and asked how many should be human.

My answer? Just about all of the NPCs should be human. Definitely at least 50 percent. Maybe more like 90 percent. This holds true not only in general settlements, but across the game world. And I think this is true across Pathfinder, Starfinder, D&D, and most other games. (Obviously, there are specific exception; an underground dwarven city should be mostly dwarves, of course, but I'm speaking in generalities.)

In a world with so many wondrous types of people in it, why stick to humans? Why intentionally make humans the dominant majority in the background?

The answer is because players want their characters to be special. They often pick strange ancestries because they want to be interesting and unique; they want to be the only catfolk in the room, and they'd be disappointed if there happened to be another handful of catfolk player characters they didn't expect, a catfolk running the bar, a catfolk selling magic items, and so on. Having the background be nearly all humans lets these characters stand out more. A couple of human NPCs saying, in effect, "wow, you're one of those rare catfolk!" makes the player feel like their character is something special, and that's just not something an NPC would say in a town with lots of ancestries (including catfolk) all jumbled together.

Anyone playing a human doesn't expect to be special just for playing a human; it's other aspects that make the human interesting and unique (is a monk in an Arthurian setting, was raised by wolves, whimsically sets things on fire, and such). They're fine if the background is nearly all humans, because they haven't chosen to stand out merely for their ancestry.

You're not being bland or lazy by putting lots of humans in as background characters in your world. You're allowing players who've selected non-humans to live larger against the background, and that's more fun for them.