I think because is useful for 3 letter agencies on ID target meetings (read Binance’s SEC suite fillings, most is based on “streams from a signal meeting” where was evident CZ had a meeting with some employees and said meeting) transcript never was submitter to the SEC indeed Signal exposed CZ to SEC prosecutors (by phone number association, not content) of course this is matter an lawyer may render moot in N ways, but exposes Signal major weakeness: user phone number correlation