Like come one it the only that does not have not one heartless.

They come from the darkness in people's hearts, right?  Unless Owl has a very dark past that he hasn't told anyone about for once, I don't think that anyone there has any real darkness.

Because even the Heartless know that mucking around with Winnie the Pooh would cause every player to unleash a fury unmatched by anything they've seen before.

From a meta standpoint, it's just supposed to be a filler world that's only there because of how nostalgic and relaxing the world of Winnie the Pooh is. From an in-universe one, it's probably just because it doesn't technically exist as a "world", so there's no heart to attack.

It's a world inside of a world and generally hasn't had a chance for the Heartless to invade it. It's kinda like Space Paranoids in that sense. The only reason the Heartless entered that world is because Ansem SoD made it happen. He re-activated the MCP and the MCP proceeded to do what it does.

 

But the 100 Acre Wood storybook hasn't really had a chance to be infested by the Heartless until KHII, and Sora saved it. It WAS damaged, though, which caused Pooh's memory to get all fuzzy, but beyond that, there really was no chance. It's been very protected besides.

Because Mini-games

Because 100 Acre Wood is childhood itself, 100% innocent, as well a hidden in a storybook. 

Unless Pooh is a secret ax murderer, there is no cause for a Heartless to be there. 

Because even the Heartless know that mucking around with Winnie the Pooh would cause every player to unleash a fury unmatched by anything they've seen before.

This works too ^

It is too much work for the heartless to tackle into. They have to steal the book, shrink themselves, and open the book only to be harassed by Tiger who would challenge them to a bouncing game and Pooh who would ask them for honey. That is too much for their mental capacity. 

 

But they managed to rip the pages in KHII

Because the Heartless don't know how to deal with a creature who needs to think about what to think about.

Because Winnie the Pooh

DARK EEYORE

DARK EEYORE

you forgot the nipples

DARK EEYORE

 

Are you Rob Liefeld's protégé?

I personally think it's supposed to be a break from all the heartless fighting and stuff. I mean why else does it have mini-games?

I pretty much agree with their was no one the Heartless could really mess with, sure, their was Eeyore, but how many Heartless would be drawn just by one person? Plus we have to presume that the kind of darkness one ahs affects the Heartless that forms, so for all we know, he'd result in Heartless that are barely mobile, etc,.