Why?

• Developers and ISVs should be able to use the development environment of their choice without limiting their userbase to users of a particular desktop environment.
• Users should be able to choose the best applications, regardless of their desktop environment.
• Interfaces between applications should be well-documented and well-defined, so they can be supported compatibly over the long term.

Modularity, documentation - it's just good engineering.

Choice is good; users and developers should be able to choose the environment and applications they like.

Fragmentation is bad; choices should not come in bundles. If I choose Windows, I should not have to choose Internet Explorer.