Hah, maybe its the difference between why as in "this addresses problem X" and why as in "because those jerks in pre-sales sold another imaginary product"

I think the commit ought to describe the purpose of the change in terms of its result for the software's intended use. Feel free to hide the business/political drama behind a ticket number.

This gets down to a more fundamental tension. Are commit messages to communicate between developers? To communicate from developer to consumer? Or some kind of project manager golem? In practice, it is usually some constantly wandering attempt to be a blend of these.