You shouldn't need to own a champ to earn key fragments

This is a bug known by Riot, and they are working on it.

Note: There's currently a bug which prevents you from earning key fragments if you're playing a champion you don't own. This is unintended, and we're working on a solution.

https://support.riotgames.com/hc/en-us/articles/207884233-Hextech-Crafting-Guide

Towards the very bottom of the page.

Why?