Why? Because people with bad judgement were mercilessly brow-beaten into developing better judgement.
We had lots of different styles of code hanging around, and you could tell if code had been written by our CTO, our leads, different guys in different teams, etc. The one rule was "write like a chameleon, and make your code look like the code it is in." (okay... to make that work, the other was "spaces, not tabs")
The code was generally very readable, and it was a very adult codebase. The problem with hard rules is that comprehensive codification of complete rulesets is fundamentally intractable. You're always going to run into areas that don't fit, or the ruleset will be laughably overwrought (and, thus, impossible to put into practice).
You could call it the code-zealot incompleteness theorem...
Of course, if I get to make all the rules and have no obligation to be complete, consistent, or considerate, I can get on board with this plan.
I bounce between many code bases in multiple languages, and this has always been my rule. I first figure out why/how are things done, and then do them the same way within reason. If the existing code has something done in a way that is no longer valid/correct, then we have discussion about changing all of the code.