> Games like these evolve their content over time

This is true, but the issue is not with the content, it's with the ability (or rather inability) to access any of the content past some point. Even if only the latest content is left accessible after EOL, it will still be better than having nothing at all. The older content can be added back, no matter how finicky it can sometimes be.

Regarding the dependencies, no one is forcing the developers to release closed ones, you can replace them with stubs. But it will be beneficial from a developer to think about it beforehand - how they will implement online systems with additional requirement of EOL etc. It's not an implementation problem, but rather an architectural one.