It's obvious why. Besides, Georgetown has been a Catholic university in name only for quite a few years now, and it should hardly be considered "according to the Catholic tradition," at this point. So, outrage, Yes. Surprise, not really.
What many people don't realize is that Georgetown is arguably not even a Jesuit school any more, because ever since 2001 the university's president has been a lay man (John DeGioia), not a Jesuit.
It is certainly not a good thing that G-Town invited Sebelius to speak at their commencement, especially given the climate between the Catholic Church in the United States and the and the administration in Washington, to which Sebelius belongs. Moreover, it is hard to see their behavior as anything but an insult, given Sebelius's part in orchestrating the HHS Mandate, that sparked the current tensions between the government and the Church. However, it is a good thing Catholics should be disappointed, to say the least, over Georgetown University's pitiful decision to invite the HHS Secretary to speak at this moment. I personally do not think this state of affairs does anything to help Katherine Sebelius or the Obama administration right now; it only fules the fire (regarding the outrage, I ought to add, it comes better late than never... see video).
Please, be sure to sign the Cardinal Newman Society's petition to have Georgetown University rescind their invitation to Sebelius. Thank you!