If i'm honest it makes sense the admin should do it. For the person invited to uninvite themselves after is a bit weird.
Imagine if someone could invite you to a calendar event, but you can't clear it from your own calendar if you say no. How does that make sense?
If I invite you to my party and you agree, your not allowed to leave before I allow you. Yours sincerely, Vlad Drăculea
That’s the best part about these problem reports on HN: It answers those Why would and Who would questions.