I can now offer my personal experience that casinos do in fact make customers fill out W9s before cashing in chips from a very successful night of blackjack.
Yup. I don’t gamble but have lived outside the USA for 8 years (and did not set foot in the US for at least 3 of those years). I still pay more in tax to the US than the average American earns… and yes it is grossly unfair as I use no US government services.