I'm going to take a wild guess as to the "why." You can see by my previous post, doing something yourself, on your own website, is really a trivial task. So primarily, anyone can do this.
I hinted that if you make it public, it is likely to get hammered. By this I mean, automated bots or scrapers will use this area of your site, and ONLY this area of your site, not visiting other areas which provide you revenue, and place a load on your bandwidth without return.
So it stands to reason - why would I want to make an XML whois feed that will tax my bandwidth for very little or no return, especially since anyone can do it on their own server?
That would be my guess <shrug>.