When we're tired of the same old

I have to say, it's refreshing to see a fantasy-setting that explains why the same human races are in this setting as well as others.

The War of Powers series was, you know, basically pr0nz but there was thought to its worldbuilding, among which a notion that its humans dropped in from elsewhere. Same with Riftwar, although it did less well at explaining how everyone got to Midkemia in the first place (maybe this is mooted in later books). Same with the Pern series. (Although here with more a SF touch. In the 1970s there wasn't that split between epic fantasy and science-fiction as we have now.) Now I think on't, same with freakin' Narnia. Much of Beyond Countless Doorways deals with worlds what aren't human, so the humans what are there are explained as later arrivals.

Another trick is to have the races be different. Blue or green skinned humans has been a SF/F mainstay, although meh. More to the point what they call an "elf" in Faerun is not at all what they have in the Accordlands. I always wondered what might happen if those elves should meet.

I suppose I'm overthinking it some. With the "planar" model, some universes are just parallels to each other, so will cough up similar races. But there are a lot of same-y Prime Materials in fantasy fiction. If a world is already stuffed with nonhuman sentients, it cannot hurt to add a backstory for how the humans (or dwarves, etc) got there.