Why Do People Leave Their Calendars Unattended?

Why do people allow "Calendar Gremlins" access to their calendars? Don't they know that these gremlins are involved in trickery? Calendar gremlins are the only explanation I can think of to account for meeting dates mysteriously being removed from one's calendar. I see someone put a meeting date on their calendar, I hear that same person agree to a date, yet when we talk about that same meeting date a few weeks later, the date has been removed and according to the other party, the meeting date never existed. That disturbs me! Did a gremlin get a hold of your phone, remove the meeting date, and wipe your memory?