As far as I understand, the WHOIS system was made in the 80s when it was useful to be able to look and ring someone up. Literally everything was in beta on the arpanet, and direct communication makes debugging a lot easier. But it's 2018, and I do not want 4chan to be able to look up my home address in that system. That creates more mayhem than it's worth by far.
Thinking about what use I ever had from the whois system, I guess it's only abuse email addresses for IP addresses. And I hear that people make use of the registration date of domains to calculate spam scores. Neither of those require the registrant's private information to be in there.