I think it comes down to Shu Ha Ri . Shu Ha Ri are three kanji that describe the cycle of training. Shu, the first stage, is building the technical foundation of the art and loyalty to a single instructor. Ha, the second stage, you must reflect on the meaning and purpose of everything you have learned. Ri means go beyond or transcend.
Students get to a certain rank, and then it's the dangle the carrot philosophy.
No matter how close they get they're not going to be able to reach it. Shihan seems like a private and exclusive club. You have to have been born in Japan, studied with the founder, or trained at Hombu to achieve a certain degree. Don't let yourself get trapped in the Shu cycle of your Aikido training. This is why you have new organizations springing up.