Calendar not syncing between two iPhones with the same AppleID

Calendars are enabled on email accounts, and calendar settings, but it still does not sync between phones (and quit syncing to my MacBook pro a long time ago). Everything else related to Apple ID sycs fine (reminders, notes, etc.). My frustration level is rather high. If I have the same Apple ID on all the devices, competent software programming should allow my calendars to sync without all these unnecessary headaches. I really can't understand why Apple isn't competent enough to address this problem. This is inexcusable.

At a minimum, it should provide some feedback while using the apps with clear indications of why two or three devices using the same Apple ID don't sync. After following the steps on the Apple help pages precisely, and the problem persisting, I have no way of knowing where the problem is. I think the evidence is pretty overwhelming that this situation should not exist, and if there is some simple solution, that should be included in the Apple support pages, instead of providing no information to correct this defect.