@Riot, Why do post-game rewards (Mastery, IP, LP, etc.) seem so skewed based off of win-loss?

I'm wondering if there's an actual purpose/philosophy behind this.

It seems like you can go 0-10 but still win, and get 15 LP, or do everything in your power to carry, play excellently, but still lose, and drop down 20 LP? This trend seems to go for IP and a few other rewards as well, which makes it really frustrating trying to climb, save up for a champ, or master a champ.