Having dealt with US Federal Government customers and multi-year projects, I think the issue is that it gets really hard to provide an accurate cost and time estimate for the whole project without a BDUF, at least once a project gets beyond a certain size.  This is especially true when the project is just a piece of a larger product and needs to coordinate with other subprojects.<p>It may be that agile is just not appropriate for such projects, in which case I wish companies and customers would stop trying to force-fit them.