Playing devil’s advocate: calendar events happen at a place and time, and they have a finite, nonzero duration.

Tasks are things that one should do.

A reminder reminds the user of something at a specific time or perhaps at a heuristically chosen convenient time in a range.

So a satellite flying directly overhead or someone’s birthday or simply wanting to be reminded of a fact on a day is not a task. There’s nothing to do, and checking it off makes no sense. (Although wishing someone happy birthday could be a task.). Simply showing the user the reminder accomplishes the goal. On the other hand, most calendar programs struggle with events with no duration, and overlaying reminders onto a schedule makes the schedule harder to read.