Why is team builder not available until level 25?

I feel like this does nothing but create a terrible experience for new players. Blind normal games are really chaotic in champ select and most of the time, if someone wants a role more than you, they will take it by any means necessary, including sometimes afking in game just because they're pissy about not getting the role. Draft games aren't as chaotic, but aren't available right away, and to unlock them you need to own 16 champs which is SO HARD to get with ip unless you're buying really crappy cheap champs. I can understand the rule for draft, not wanting your entire champ pool banned away, but why tb?

Why are new players not allowed to queue up for team builder and learn their favourite champ? New players are exposed to an incredibly toxic environment in game already due to the fact that they're not as good as all the smurfs they get matched with and against, but teambuilder is a place to try new things and learn. The only reason I even use teambuilder is to try new champs or new builds. If I wanted to take it seriously, I would queue into draft or ranked, where there are bans.

It just doesn't make sense to take this away from new players. What's the reasoning behind it?