Just open sourcing the actual engine wouldn't do much. At best, you'd be able to make it work on newer hardware if problems arise, or port it to other OSs. Great stuff, but not enough when it comes to improving the game, preserving multiplayer, and so on.
There's a great amount of scaffolding on top of the base engine that any moderately sized game implements, be it through scripting or native code. That's what I meant by the line between the engine and the game being blurry. If you want to make meaningful changes to the game, you need access to that framework portion, but releasing it would allow for easy reverse engineering of everything else. It's a difficult balance to achieve.
Yours is a flawed, extremist view.
How impressive something is has nothing to do with whether or not its source is available. What, if they release it to the public it suddenly becomes impressive?
You can disagree with the method of distribution, but it doesn't affect the quality of the game.
Piracy being a thing isn't a strong argument for open sourcing everything, since the barrier of entry is higher than you may expect for non technical people, a barrier that would definitely be lower if any game was freely available and compilable by anyone. Someone will make a free, one click installer, guaranteed.
Now, can you charge for open source software? Definitely.
Will it generate significant revenue in most circumstances? No.
Open source software relies on two methods for funding:
The former isn't something one can stably rely on, the latter just isn't applicable to games.
Again, that model can work for some high profile projects, but in the vast majority of cases, it won't. Especially not for games.
One can make works of passion and still want to be compensated, that's what artists do and games are a form of art. You clearly never had to put food on the table with the art you make.
Your vision of everything being open source is a utopia. A noble idea, for sure, but reality is a cruel mistress.