Abstraction is a trade off. You don't want to build interface layers between everything... It's a pain in the ass, and if there's a 1-1 relationship between parts of a system then you're basically putting in a minimum cost to modify that area in any way. So if you do it, it'll probably be once you've locked down the design pretty well

Game development is pretty different than normal development too. You have a lot of one off and lose ends based on creative decisions... You aren't building up on top of your system, you're building out

And frankly, it leads to a mix of mind blowingly good code and a lot of terrible code

So no, I don't think it's that easy. I think it's also a bullshit argument, and they should release the "proprietary" code when they finish supporting the game, or put in the time to make the interfaces