Too hard to keep track of and even if the tracking was easy, I'm not spending 12 hours of my life every month going through the mod client and the FAF user list to hand out the avatars and take them away from the last league's winners. Someone wants to make some automated program that does it and doesn't require my input? Fine. I wouldn't even give someone mod client access to do it manually because they will get burned out in 2 league seasons and then I'm suddenly the dude that needs to take over doing it.
I'm not interested in separating the king and prince avatars from the league system. If there is 0 interest in 1800+ players getting the king avatar by playing 20 minutes on ladder, what even makes you think they would go through the tribulations and effort of an entire tournament?