Author here! You probably just don’t have the same need as me, I was expecting this to not be a popular app because of this :)

My need is to be able to check when I’ll be able to visit parents, plan trips with friends, answer my wife about when’s our next dentist appointment before she gets tired of waiting and checks it herself, when’s our niece’s birthday, what is the next religious holiday etc.

I find I have to check the calendar way more than I have to add something into it. And when I need to add something, I usually like to take the time and fill in useful info like location, travel time, useful URLs and notes. And Calendar.app is already good enough for that.