Why do I have to enter a "Registrant" for .AT domains?

Nic.at, the central registry for .AT, requires that a registrant is set when a domain is registered. You can specify an organization, person's name, or both. If you specify a person's name, it must be between 2 and 5 words in length, with at least 2 of the words longer than 2 characters.

NOTE: The registrant can only be changed by placing a .AT domain trade order along with submitting a change holder document signed by both the current registrant and new registrant.