Brian Jones has a blog post entitled Politics behind standardization where he writes

We ultimately need to prioritize our standardization efforts, and as the Ecma Office Open XML spec is clearly further along in meeting the goal of full interoperability with the existing set of billions of Office documents, that is where our focus is. The Ecma spec is only a few months away from completion, while the OASIS committee has stated they believe they have at least another year before they are even able to define spreadsheet formulas. If the OASIS Open Document committee is having trouble meeting the goal of compatibility with the existing set of Office documents, then they should be able to leverage the work done by Ecma as the draft released back in the spring is already very detailed and the final draft should be published later this year.

To be clear, we have taken a 'hands off' approach to the OASIS technical committees because:  a) we have our hands full finishing a great product (Office 2007) and contributing to Ecma TC45, and b) we do not want in any way to be perceived as slowing down or working against ODF.  We have made this clear during the ISO consideration process as well.  The ODF and Open XML projects have legitimate differences of architecture, customer requirements and purpose.  This Translator project and others will prove that the formats can coexist with a certain tolerance, despite the differences and gaps.

No matter how well-intentioned our involvement might be with ODF, it would be perceived to be self-serving or detrimental to ODF and might come from a different perception of requirements.   We have nothing against the different ODF committees' work, but just recognize that our presence and input would tend to be misinterpreted and an inefficient use of valuable resources.  The Translator project we feel is a good productive 'middle ground' for practical interoperability concerns to be worked out in a transparent way for everyone, rather than attempting to swing one technical approach and set of customer requirements over to the other.

As someone who's watched standards committees from the Microsoft perspective while working on the XML team, I agree with everything Brian writes in his post. Trying to merge a bunch of contradictory requirements often results in a complex technology that causes more problems than it solves (e.g. W3C XML Schema). In addition, Microsoft showing up and trying to change the direction of the project to supports its primary requirement (an XML file format compatible with the legacy Microsoft Office file formats) would not be well received.

Unfortunately, the ODF discussion has seemed to be more political than technical which often obscures the truth. Microsoft is making moves to ensure that Microsoft Office not only provides the best features for its customers but ensures that they can exchange documents in a variety of document formats from those owned by Microsoft to PDF and ODF. I've seen a lot of customers acknowledge this truth and commend the company for it. At the end of the day, that matters a lot more than what competitors and detractors say. Making our customers happy is job #1.