"How [does it] come [about that] you guys never play poker with us?"
or, to use an archaism that wouldn't fit in that context
How come[s it to pass that] you guys never play poker with us?"
I'd have to do some research to be sure, but this sounds to me like an Americanism introduced into English by European immigrants - like 'what gives?' and 'by me' (German Was gibt es and bei mir).
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