Probably not in scope for Project Zero? Or they find other stuff more interesting.
Security researchers don't work for free. I did some light searching and I couldn't find any sanctioned audits against Bitcoin core. The Bitcoin team should hire someone like trail of bits to do a multiple month audit.
But the "security researchers" wouldn't be working for free. Bitcoin has had an enormous bounty on its head for at least 10 years: "hack me and get paid millions/billions". It would be naïve to think there aren't highly skilled people continuously trying to do that.
Security researchers don't work for free. I did some light searching and I couldn't find any sanctioned audits against Bitcoin core. The Bitcoin team should hire someone like trail of bits to do a multiple month audit.