You think Rob Pike and Ken Thompson made what you consider a mistake out of ignorance? Just because you don't like it doesn't make it a mistake.
As far as I know, these guys have a reputation in industry moreso than in academic circles. It seems entirely believable that they have taken no interest in language design outside of industry, where the state of the art lags a few decades behind that of academia.
Consider all the error-checks in Go -- these are all incorrect from a boolean-blindness perspective, and that would be a lot of code to rewrite if they add proper constructs to Go. Thus, I really believe it is just a mistake -- one that is only possible to make out of ignorance.