If you're in the market that doesn't respect copyright law there's a surprise for you - no one will buy legal copies of your game either, and it will be banned everywhere else.

Also code for the game itself means almost nothing without the tooling to produce assets for it. It could be written for scratch but then....just.....use unreal or unity? Pirate copies if you really don't care. Like, I work in games development and in house engines are incredibly inflexible, they are made for one game only usually and it's a titanic amount of effort to use them for anything else. You could probably use the Witcher engine to make a crappy clone of Witcher, but you're not going to use the engine for anything else.