I think its simply a product of scale and the traditional background from the 2 camps.
If you look at where the microsoft development culture has come from, it is around smaller, 'frontend' apps with a short lifespan, put together by teams of 1-5 people. The priorities for tools, frameworks etc are strongly based on productivity; maintainability and the long-term view were secondary.
If you look at the heritage of java, it is around 'backend' apps with a longer lifespan put together by large, often distributed teams. Maintainability and the long-term view take precedence over cranking out working, pretty systems quickly.
The concept of architecture and clear separation of concerns only really adds significant value when you cross that magic threshold somewhere in the middle.
Now that DotNet, C# and associated frameworks are moving into ground traditionally held by Java, we're seeing an increasing interest in the concept of architecture from the microsoft side - witness the 'Architecture edition' Visual Studio tools coming through in recent years, their 'Architecture Journal' and so on and so forth.
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