Team Builder Locked?

I want to know why Riot decided to lock Team Builder for those who are not level 25 yet. I'm trying to play with new players who want specific roles and it's not easy doing it when I'm trying to spam their role in Blind Pick >.< And please give legit reasons, not the reason that it's "unfair" or "unbalanced" if you have new people and let's say diamonds playing together because just possibly the diamond is teaching that new guy how to play without having to go into bot games.