Why was Harlem a desirable destination for Malcolm?

Coming from the rural, primarily-white Midwest, the young Malcolm Little was taken in by Harlem's expansiveness, diversity and nightlife. Having been one of a few Black families in Lansing, Michigan, the Little family experienced regular harassment from members of the Ku Klux Klan and other white nationalist groups, which eventually culminated in the murder of Malcolm's father Earl and the subsequent collapse of Malcolm's family. In New York, specifically Harlem (which was predominately-Black at the time) Malcolm found himself no longer a vulnerable minority, but part of a connected, established Black society who dominated the clubs, bars, restaurants and most other aspects of city social life. After being released from prison in 1952, Malcolm would establish a temple in Harlem due to its large Black population, accessibility, and geographic desirability.

While he was in prison from 1946 to 1952, serving a sentence for robbery, Malcolm X learned to read and converted to the Nation of Islam. Harlem was a desirable location for him after his release because it was a center of black life. He went there in 1954 to found a temple for the Nation of Islam. He established Temple No. 7 in a storefront, and it grew rapidly. Later it moved to 102 West 116th Street.
Because the Nation of Islam was a black separatist movement, it made sense for Malcolm to locate temples in places with large black populations. The idea was to create a society independent of white culture and to inculcate black pride. Malcolm X established Nation of Islam temples in other cities, but New York's Harlem was a logical place to build the movement.