(white) man in the 1960s, which is sexist
You're joking, right?
The methodology was developed by a man who read the available literature and based on our understanding at the time created a model.
Since the method was developed we've invested in research for better models but it isn't a case of just changing the thermostat, which would be sexist and racist. We don't understand enough about many of the parameters, there's a lot of unpredictable elements and with current social climate it's near impossible to push to change the existing standard because it's a risk supporting the necessary framework and/or changes.
An outcome that doesn't instantly equitable isn't inherently sexist or discriminatory.