It’s odd you used SimCity because the expansions are two skin addition bundles and updating the modding tool.
I think I understand what you’re trying to say, but “feature complete” isn’t the term. While “stuff was added” to boxed copies back in the 80s and 90s, it wasn’t to the degree you see today.
Also consider most boxed copies didn’t see updates. They didn’t until the early 2000s because most people didn’t have (reliable) internet access. Hell I played a different version of Counter Strike than a friend of mine for months because his internet was awful and his download kept failing.