Why do I not win as much ELO as I lose?

[RedAlert39]

You'll gain more ELO for beating higher ranked players, and less ELO for beating lower ranked players. You'll lose more ELO for losing to lower ranked players, and loss less for losing to higher ranked players. As JackNapis pointed out, the only factor that will fudge with these numbers is that new players will have a higher K factor, which means they both lose and gain ELO at an accelerated rate (the intention is to allow them to reach their true ranking more quickly). If you're comparing across games where you have different K factors, then your ELO gain/loss could seem inconsistent as well.

But for the most part, your games will conform to those rules, and all of your examples show it too.

Then there is this 5 player game I won... Fine, I was highest ELO but two players were close to my ELO and I only received a fraction of their lost ELO

Me 321 + 16 = 337
P2 151 + 17 = 168
P3 303 - 3 = 301
P4 201 - 18 = 183
P5 309 - 48 = 271

I mean sx@t, P5 alone should have boosted me more. And merely beating 4 other players should have as well.

If you mouse over your ELO at the game-end screen, you can see the breakdown:

Details of the ELO calculation for purefct
ELO rank before this game 321.32
K factor 10
Victory against Noaros
151: Probability of a win: 73% 2.72
Victory against Claeys Ivan
304: Probability of a win: 53% 4.75
Victory against jgpaladin
201: Probability of a win: 67% 3.33
Victory against Tingji
319: Probability of a win: 50% 4.97
Total ELO variation 15.77
ELO rank after this game 337.09

Because you've played a lot of games of Hawaii, you have a lower K factor, which means you aren't gaining or losing as much ELO as you were before. When you were at 20K, you were gaining/losing 10 ELO against a similiar ranked opponent. Now that you're at 10 K, it's only +/- 5 ELO.