To hide / mask it is much different than to not post it on your web site. I agree that such information is important - and should be provided if asked. But just because YOU need to know doesn't mean an instructor has to post on their site. Nor does it imply that they are under qualified. If they have an address, show up and ask. If they have an email, write and ask.
I don't have it on my site - thought it would be boastful to do so. I can provide it if asked though. If it's relevant, and if I'm asked nicely. If demanded, I wouldn't share my favorite color with ya.
This is my pet peeve ... in the martial arts who your teachers are seems to me a pretty obvious piece of information, and when it is missing one does start to wonder why...