Ok, to my knowledge, I am sure a few individuals have been disappointed about not being able to make a Naruto Uzumaki biography. That being said, I do not think that his restrictions are impacting the RP activity to even a fraction of the extent you believe it may be. There are an endless number of possibilities for biographies, as there are dozens of other Naruto-verse biographies and of course, custom bios. Yes, there are tons of possibilities out there, for new and old RPers alike.
Naturally, the test needed to have a Naruto Uzumaki biography is quite difficult. Of course, just like the other eight jinchūriki biographies, there is a great deal of power inherently possessed by each of them. The way the RP goes about restrictions is typically based off the sheer amount of abilities/powers a given biography, by default, has. I'd like to emphasize that most, if not all of the jinchūriki biography tests have been passed at one point or another. I am aware, for instance, that the Naruto Uzumaki test has been passed twice by the same individual. All in all, it wouldn't be fair to make only one jinchūriki something that anyone acquire. The goal is to test the limits of the individuals whom desire it and showcase their skill, which has worked to an extent as four jinchūriki biographies are in use right now. No shortcuts.
Going beyond just what has been mentioned above, there is the issue of the logistics. Your proposed idea is to have everyone pass a series of progressively more difficult tests, numbering over half of a dozen. The influx in people demanding tests would be highly problematic as testers are already often dealing with a fair number of tests. Essentially, too many tests would derail the pace of all other tests, which in some cases are fairly slow to begin with and testers may only accept a few tests at any given moment, until completed. Having biographies limited to only 1-2 tests helps everyone.
In conclusion, to make merely one of several biographies free to anyone, there are several issues bound to be incurred. At it's core, it goes against the RP establishment and making an exception for one biography wouldn't be fair to others and whatever biographies they are testing for. Certainly, the biography approval and testing process would plummet harshly.
To those who would like to possess the Naruto Uzumaki biography, just give it your best and hope your endeavors are satisfactory. People have done it in the past, why not now, in the present? Show this site just how skilled a RPer you are.