I’ll start the discussion.
No one knows, it’s one of many mysteries about the development of poker. There is no evidence of connection to earlier games. The card play is based on common principles and could have easily been made up on the spot by any experienced card player in the late 1700s or early 1800s. It is the betting structure that is unprecedented, and by the time it is first documented reliably in the 1840s, it was fully developed, likely as a result of many decades of refinement, completely outside the general evolution of card games or gambling.
The argument against a derivation from a foreign language is it was never spelled any way but “poker”—unusual in an age of limited literacy—and never hinted of an unusual pronunciation. While there were many variants distinguished by adjectives, there was never any dispute that they were forms of poker, subject to poker principles. Moreover, from very early times it was widely reported that the game was common in the American Northwest (what we’d now call the Mississippi Valley region), and virtually unknown outside it. It was considered to be a game native to those parts, not an import or variant of another game.