@gibberishcode - They have made some efforts to provide greater transparency, example:
https://tether.to/wp-content/uploads/2017/09/Final-Tether-Consulting-Report-9-15-17_Redacted.pdf
It is concerning that these reports aren't coming out more often, but I think there might be concerns about disclosing too much information to competitors (and regulators) about where and how their money is being held.
Crypto is in an uncertain time where there's a great risk of government regulation or asset freezes for connections to illegal activities. Disclosing their banking information to too many parties could put Tether at risk.