Opted for large scaled systems. It’s more than just simple software. There is a ton of infrastructure and proprietary solutioning that goes into it. That’s likely used for other games as well.

Doesn't mean it can't be released, just that it might be difficult to reproduce. It would still be much, much easier to reverse engineer that than to reverse engineer everything from the client and network communication captures.

It may not even be possible to release the software because it is not just software and the resources to prepare it for releasing may not be available.

In other words, so you don't know, and vague assumptions on a closed box because closed boxes allow you to make them.

Most MMOs usually have multiple instances running, each which need to be maintained separately. That means they have usually gone through the process of encapsulating the server functionality in a way that can be reproduced and recreated into new instances. They have to be maintained at the same time, so they need to be relatively standard. At one point those supposedly absent resources to duplicate the instance of a server have likely existed, and just need to be packaged for public release. Proprietary portions can simply be excluded - an incomplete release is preferable to an absent one. Can't release databases, they can release schemas, etc. Incomplete > absent.

You largely seem to be giving MMO companies the excuse that if their server solution could theoretically be proprietary and convoluted enough, even if it really isn't, that they not be subject to the Stop Killing Games initiative. MMOs, unlike single player games, have a far more notable sociable and persistence factor to them, a bigger cultural footprint within those communities, that makes the Stop Killing Games Initiative particularly applicable to them. There's one simply way not to be subject to its demands - don't kill the games.