Because if you look at GoDaddy (probably R) domains that are "privacy protected" you see the registrant is actually "Domains By Proxy, LLC" and switching that domain to another GoDaddy account would be invisible on the whois system.
It's still a silly setup - but then again, we have the same thing in banking - I could send you funds if I know your routing and ACH number (which is available on any of your checks, etc). So if I were a big crime lord I could randomly send money directly to people I didn't like so they'd go down with me.
There are available for $5 per year but need to publicly show your details