Perhaps (inasmuch as the assumptions behind this question are even correct) because North American society itself is so ghettoized.
The assumptions of "accessibility"--that our own attitudes determine our currency with the masses--are flawed. Some anarchist circles behave in a completely closed and exclusive way, others are extremely, even excessively inviting, most are in the middle, and all of them are isolated from society at large, with only minor degrees of difference. This is because all individuals, and society itself, is isolated from society at large, in North America more than in most places.
The masses constituted by capitalism have been atomized and banished from the streets. The only remaining mass is virtual. In social terms, anarchists tend to be less isolated than the average American. They can often count more relationships of trust and their friendships tend to be more supportive materially and emotionally than the ideal middle class citizen.
To question another of your assumptions, I must say that ghettos are sites of resistance and togetherness cordoned off by a repressive order. The walls currently are not made of concrete and barbed wire, but they are still there. I suspect their principal ingredient is electromagnetic, the same stuff that moves through iPhones and youtube.
