While we don't currently know in canon as far as I'm aware, back before the Disney buyout, there was a planned novel called Alien: Exodus, which would have explained that humans had been taken from earth, and turned into slaves. Though they staged a successful revolt against whoever enslaved them. Granted, since that was canceled, it's not canon to either legends or canon. But it's the best explanation we have.

Oh that's interesting, I didn't know that!

I feel like I read somewhere that humans first came from Coruscant and expanded outward over thousands of years.

That would make sense, but I can also see Naboo possibly being their home planet.

I believe in Legends they’re said to come form Coruscant.

^ Yup. In Legends, Human ancestors come from Coruscant.