Can someone explain to me why we don't get champion points for 3's?

I don't really play 3's anymore, but I'm genuinely curious: Why are champion points not counted on 3's? I scrolled down to 3's just to examine it and it indicated that I'd be getting IP/XP and that's about it. This is the first sentence on the article about champion mastery:

[quote]Finish a game of League and you’ll earn points for your champion based on your team’s performance as well as your own contribution.[/quote]

So, am I missing out on something, or does 3's not count as a game of League? I can understand this thing not counting with ARAM, since you get random choice on champs, but in 3's, you can choose. Any reason why people can't get champion points for those games?