Well, to eliminate a source of spam, reduce exposure to phishing, and prevent vulnerabilities like the one talked about in the article by reducing attack surface.
If someone is going to make some demand for my time, the very least they can do is give me notice outside of my icloud calendar. An email, an IM, a phone call, etc are all very easy and they allow me to make sure it's real before it has any chance to interfere with my schedule. "Hey Boss, this guy says he's our new IT guy and he wants to talk about my network settings" or "Hey $vendor, I just got a call from $rando saying he's our new contact, can you verify that for me before I tell him everything I know about your propriety applications?"
It helps that I like to keep my work devices and my personal devices entirely separate. If someone in the office wants to pull me into a work meeting through outlook, they'll already have to have an account set up on the company's exchange server. Anyone outside of the company I should already have a relationship with or at least a heads up.
