A lot of things are generally accepted as "good ideas", but how often are they practiced? Most software management would throw their own mother under a bus if it got the product out the door on anything close to schedule or budget.

Which is to say, code cleanliness is very much not the norm anywhere. And if anything the game industry seems to be a good 10-20 years behind the rest of the software industry in terms of hewing to good practices (clean code, automated tests, etc.)