I have 14 calendars logging approx 500 events per month, and I have a UI for all of this... Google Calendar.
I also have API endpoints for all of this... Google Calendar. Which can be triggered by IFTTT for automatic stuff (i.e. did I Instagram something or Tweet?).
My email is linked to Gmail, so flights, itineraries, online shopping delivery, restaurant bookings can all flow in.
So the only thing I need to do manually are the few things it cannot automatically know, such as what film I just watched or what book I finished reading.
I only log public things, that is... data that exists in someone else's database somewhere. I do not log private things, i.e. Signal conversations or anything 100% offline that didn't involve a public database.
For me it's a simple thing... this data exists, can I make store it myself in a structure that I can do something interesting with it.
I have about a decade of this data.
Oh, and Google Calendar is really long in the tooth and is becoming both slow to use, hard to search, and clunky.