Apple iCloud

Apple products are geared to make everything easier for the average consumer.

It is assumed that most people have little interest in managing an ever-filling-up-with data phone, and little interest in tracking security issues.

Apple manages this by "locking down" devices in many ways.

Apple steers you to keep large downloads (like videos, etc.) on your iCloud drive. iCloud knows what calendars are, and may actually block subscribing to calendars hosting on the web elsewhere. 

If you don't have or use iCloud, are not logged into it -  your phone may respond with no activity or response at all. 

Things that seem simple to do - aren't as straightforward on a device that is seeking to block anything slightly suspicious.