It's simply because while it's subject to her availability, any minister who is unwilling to appear before a committee to deal with the constitutionality of the system that she designed, on a deadline she designed, before that deadline expires, is not formally in contempt of Parliament but is acting contemptuously before Parliament. Morally, she can clear anything off her agenda, aside from some kind of personal health crisis or tragedy in the family, to be here. Therefore, she should darn well make herself available, and I want to make that point by voting against this amendment.
That said, if the government pushes the amendment through, I'll then be voting for the main motion as well, and I'll be asking that we make every effort to get her here next week.