The main reason, in my experience, that engineers don't know the full system is due to the absence of a formal design process in almost all cough professional software systems being made. Without full respect being given to the documentation process there is no way to know what exactly is being made and for what purpose. This is partially an issue of lack of education and partially an economic/political issue - since it is 'cheaper' in the minds of uneducated project managers to cut back on design time and it is also financially beneficial for contracted programmers to be the 'specialist' who 'knows the system' since there is no real documentation available for others to read.

I checked out the link to tauchain but it's broken because they don't support https there. I then went here and reviewed the basics of what it is but I don't really understand how it relates to the launguage concepts that you have written about here - did I miss something?