Champion Mastery

It seems unfair that you cannot earn champion mastery points for champions you don't own. Is the purpose not to reward your performance or provide proof of experience with the champion? You may or may not try a rotation champion several times before buying it, and that shouldn't affect your champion mastery level. Especially now the Hextech Crafting features are up on NA server, this is even more significant, because it prevents people who performed well on rotation champions from earning a chest. I understand reward is a privilege, but it would be nice to be rewarded for a good game anyway.