I could follow it a bit. CalDAV is mostly nerd stuff. And proprietary apps use to disallow CalDav to sell their own stuff. Best example: M$ Outlook doesn’t support CalDAV natively. You can only add them as only read, or use third party addons. And why? Because they want you to buy 365.
Look at it as the average Bob: wow you can sync all your contacts and Calenders and Tasks to every device? That must be expensive!
Ah, the goodies win. One of aristotle’s tragedies. Classic.