Let's take a trivial problem: holidays. Every account you have comes with a holiday calendar. So if you got a Microsoft, Google, and Apple account you'll have entries in triplicate. These are all day events with identical names. There's a lot of hints to tell you that these are identical and you only need to display 1.
A bit harder would be birthdays. These might not be in a unique calendar. But the word "birthday" is a huge hint when it's an all day event.
I do agree that defaulting to a position of not destroying data is best (though here we'd never destroy data). But that doesn't mean we can't offer users assistance. We do have the capacity to let users merge events or in some way note that they are identical.
One more issue, why the fuck can't I move an event from my Google calendar to my Apple? In the worst case, just copy the damn thing and then hide the event. You can do this even when you don't have write access to the Google calendar.
So the thing I don't buy is that we can't do more. A programmer's job isn't easy. But it involves problem solving. I think there's not enough grumpy yet motivated people who will voice up such things because management usually says that it's not important. But these non important things add up. Life is complex so the little things actually matter a lot.
