Well, they left since they were being discriminated against and expected to find a better society. We can't know whether they liked what they found, however. Racism was not absent in USSR either, although it was not institutionalized.The Blacks who left the United States for the Soviet Union did so because the society they found was superior enough for them, where their talents were rewarded because of their skill, not demeaned because of their skin color, and there they made valuable contributions to Soviet society.
I would like a citation here...or a dozen citations, actually. I am extremely sceptical about this last claim. Emigration from USSR, whether legal or illegal was almost impossible. Re-emigration into US on the grounds "it really isn't as great here as I thought, I actually liked it better back there"? Unthinkable. At best, maybe some of these people were able to return as Soviet diplomats of officials of some kind.I would dare say that immigrants to the USSR, both from former imperial colonies and the West, generally found life better than where they left. The ones who didn't went back where they came. And some of those American Blacks did just that.
EDIT: I was trying to find sources about blacks emigrating from US in USSR and found this:
http://en.wikipedia.org/wiki/African_diaspora EDIT 2: Nah, this obviously irrelevant sample.During the 1930s fifteen Black American families moved to the Soviet Union as agricultural experts.
...and this book: http://search.barnesandnoble.com/The-Forsaken/Tim-Tzouliadis/e/9781594201684
Spoiler :
...The Forsaken starts with a photograph of a baseball
team. The year is 1934, the image black and white: two rows of
young men, one standing, the other crouching with their arms
around one another’s shoulders. They are all somewhere in their
late teens or twenties, in the peak of health. We know most, if
not all, of their names: Arthur Abolin, Walter Preeden, Victor
Herman, Eugene Peterson. They hail from ordinary working
families from across America—Detroit, Boston, New York, San
Francisco. Waiting in the sunshine, they look just like any other
baseball team except, perhaps, for the Russian lettering on their
uniforms.
These men and thousands of others, their wives, and
children were possibly the least heralded migration in American
history. Not surprising, maybe, since in a nation of immigrants
few care to remember the ones who leave behind the dream.
The exiles came from all walks of life. Within their ranks were
Communists, trade unionists, and radicals of the John Reed
school, but most were just ordinary citizens not overly concerned
were politics. What united them was the hope that drives all emigrants:
the search for a better life. And to any one of the millions
of unemployed Americans during the Great Depression, even the
harshest Moscow winter could sustain that promise.
Within four years of that June day in Gorky Park,
many of the young men in that photograph will be arrested and
along with them unaccounted numbers of their fellow countrymen.
As foreign victims of Stalin’s Terror, some will be executed
immediately in basement cells or at execution grounds outside
themain cities. Others will be sent to the “corrective labor”
camps, where they will be starved and worked to death, their
bodies buried in the snowy wasteland. Two of the baseball players
who survive and whose stories frame this remarkable work of
history will be inordinately lucky. This book is the story of these
mens’ lives—The Forsaken who lived and those who died.
The result of years of groundbreaking research in
American and Russian archives, The Forsaken is also the story
of the world inside Russia at the time of Terror: the glittering
obliviousness of the U.S. embassy in Moscow, the duplicity of
the Soviet government in its dealings with Roosevelt, and the
terrible finality of the Gulag system. In the tradition of the finest
history chronicling genocide in the twentieth century, The
Forsaken offers new understanding of timeless questions of guilt
and innocence that continue to plague us today.
...The desperate poignancy of the situation for many comes through in a heartbreaking letter from a teenage American named George Sviridoff, who was arrested for trying to leave the USSR and found himself in a concentration camp above the Arctic Circle. Writing to his father in the U.S., the captive American explained: "Now papa my fate is sealed. I have left you, lost my country, lost my freedom, lost all the delights of life...there remains in addition only to lose my head."
The Cold War began in the 1930s, to judge by this narrative of strange events within the borders of the old Soviet Union. It's just that no one thought to tell the Americans. British TV journalist Tzouliadis turns up an intriguing tale in the undocumented Depression-era migration that took tens of thousands of Americans to the Soviet Union, recruited for their technical skills in a time of widespread joblessness at home. They did not have to be persuaded; a Soviet trade agency in New York advertised 6,000 positions and received more than 100,000 applications, Tzouliadis reports. Few were communists or fellow travelers; most listed disgust with conditions at home as a more powerful reason than "interest in Soviet experiment" for their exodus. One reason for disgust was Jim Crow, and African-Americans fleeing racism figured prominently in the wave of migration. Once in Russia, the Americans lived as Americans do abroad. Some blended in, others banded together, formed baseball teams, searched out their compatriots-and they worried when their children seemed to be "turning out just a little too Red' " after a spell in the Soviet school system. Things turned sour, though, after 1936, in the years of Stalinist purges, when all things foreign were suspect and the elite of Russian culture and politics were killed off. The Americans, one by one, started to disappear into the Gulag. Diplomat George Kennan observed that the Soviets justified this by unilaterally making Americans citizens of the Soviet Union, thus negating their rights. "Logically we should refuse to recognize the naturalization of Americans in the Soviet Union as voluntary and valid in the absence of confirmation," Kennan wrote,but instead the U.S. government did nothing-and would do nothing when, a decade later, Americans taken prisoner during World War II, even though allies, were shipped to the Gulag, joined still later by POWs during the Korean War. Tzouliadis's narrative-though rather tuneless-holds the reader's attention and illuminates an overlooked chapter in 20th-century history, revealing larger trends in relations between Russia and the United States that persist today.
Sounds like something you might wish to read...

EDIT 3: ...and this book:
http://www.amazon.com/Black-Red-Years-Inside-Soviet/dp/0874918855/ref=pd_cp_b_2
This guy apparently got lucky... he eventually seems to have preferred Idi Amin's Uganda though...Robinson, a Jamaican-born Ford Motor toolmaker who sought economic security, engineering training, and an escape from racism, was recruited to work in the Soviet Union in the mid-1930s. Never a Communist, Robinson walked a tightrope while living in the Soviet system, not completely accepting or being accepted by it and recognizing that there was racism, repression, and regimentation around him. Finally, after 24 years of unsuccessful effort, Robinson "escaped" to the United States via Uganda. He provides firsthand accounts of the Stalinist purges, sacrifices of World War II, and economic and political tensions of the Cold War. A rare look at Soviet life.