Binance operates out of the US and I'm not confident they would comply with a subpoena. Maybe they're using some chat service with a US presence which is subpoenable -- Slack or whatever.

Maybe, but given the powers the SEC have to prevent them operating in the US financial system at all, and sanctioning anyone who wants to operate in the US if they deal with them, it’s usually less risky to hand over the data and hope they don’t find anything.