Why is Team Builder so high a level

One thing that has bothered me for a while is why Team Builder is unlocked at level 25? It seems to me that if you want to learn a champion or role, being able to pick that champion in that role over and over again with a guaranteed place in a match would be most beneficial, something that should be unlocked far sooner than level 25. Any particular reason or justification for the later unlock that I'm overlooking?