I do not recall for certain the specific reason at this point, but I believe it was to ensure that realms did not force new, and thus "untrusted", members to be courtiers and perform region maintenance work for some amount of time upon joining.
Well that would be an egregious IR violation if a realm did that. If a realm wanted to saddle newbies with grunt work knights can still perform civil and police work.
I'd suggest dialing this one back to at least the 2 week limit.
