Why people struggle at 1/2

[Clownfish]

I was looking at everyones graphs about a week ago showing excellent win rates at .5/1 and then showing roller coaster rides at 1/2. Then hearing everyone say how 2/4 is actually easier than 1/2 and it made me think about the rake schedule. So I decided to run a quick report looking at rake as percentage of pot and found that the worst rake seems to be at 1/2. Here's some stats from various sites...

.5/1
Paradise - 2.3%
Pokerstars - 2.0%
Party - 3.8%
Absolute - 2.5%

1/2
Paradise - 3.1%
Pokerstars - 2.9%
Party - 4.2%
Absolute - 2.3%

Another interesting note is just how high Party's rake is. I think they don't realize that having a higher rake is a bad idea at the micro levels. People are just learning to play and instead of feeling like they are winning players, they are just donating their money to Party. Obviously back to back WSOP winners helps Pokerstars but, I also wonder if this is partially the reason that Pokerstars is growing so much quicker than Party.

BTW, 10/20 Party rake is slightly below 2.1%