Why the (self)segregation still persists even today?

It took a hundred yearrs since Lincol declaration untill LBJ's Civil Rights Act for the black ofiicialy have the basisc rights of a civilized society, yet today, half a century after the segregation or self-segregation stiil persits! Why? Why do we see racially divided cities, the cities wich you would expect to be more progressive more liberal, more open minded?
Why even today blacks and whites don't want to interfere each other (except at the job), and don't socialise, don't hung up each other? Why it's so hard to change the way of thinking of the whites about blacks and vice-versa?
Look, even the irish and italians managed to de-enclavise and make peace one another, to mix in the same neighborhood, the asians as well...only blacks haven't!
If you look various documentaries in the '70's from NYC about white fearing the coming of the blacks in their neighborhood, judgind with today's head you would say: "oh my god, what foolish they were, they didn't know that the black also have the same rights like them and it's normal to live one next another"!