There were several prophets/saints/leaders of Islam in America and people spreading Islam who were highly charismatic would be the short answer. The Muslim groups also tended to be well organized and went out and tried to gain followers as Islam like Christianity is a religion that is big on gaining converts and proselytizing (hence why the Hebrew/Jew groups never took off as much).

Some of these people include Malcolm X, Muhammad Ali, Noble Drew Ali (Moorish science Temple), the honorable Elijah Muhammad, etc. Elijah Muhammad who was the leader when Louis Farrakhan, Muhammad Ali and Malcolm X joined was considered to be a highly charismatic leader. Who not only talked the talked, but walked the walk and went to prison and served years for refusing to fight in WW2 on the grounds of religious reasons. This garnered him significant respect and credibility within the community because people saw he didn't just talk big, he backed it up. Unlike many of the Christian preachers of that time who simply told followers to pray for better, he offered real tangible solutions to people's problem. If a person had no job, he would employ them in the many businesses that the Nation of Islam ran.

I do have some ideas on why Islam was seen as more native in that regard. West/North Africa where most of the African Americans ancestors come from had been practicing Islam for hundreds of years before West European colonialist showed up. Most likely their ancestors had been practicing Islam in places like Malian empire, Sokhoto Caliphate, Sonhai, Wagadou empire, as well for centuries. There were a few Jewish and Christian kingdoms in the region but for the most part as far as North/ West Africa and the Swahili coast of East Africa were concerned Islam was the dominant religion so this is where the American black ancestors largely had been brought from.

Further, many African Americans grew distrustful of Christianity and Christian preachers as they had learned during slavery/segregation that many of the black pastors were controlled by slave masters and had been teaching them a "slave version" of Christianity that had removed hundreds of pages from the Bible (basically anything that contradicted slavery and being obedient to white power structures oppressing them). Moreover, those preachers were often times white, or if they were black were monitored, controlled and essentially censored by white slavers then segregationist as to what they could discuss in church. As such, any part of the religion that could be theoretically used to essentially help or favour African Americans, had been systematically removed from the religion being presented to them.

A practical example of this is two passages in the bible say slavers should be given the death sentence

Deuteronomy 24:7 " If someone is caught kidnaping another Israelite, enslaving or selling the Israelite, then that kidnaper shall die. So you shall purge the evil from your midst. "

Exodus 21:16–21:16

"Whoever kidnaps a person, whether that person has been sold or is still held in possession, shall be put to death."

Instead, blacks would be presented a part of the bible that said

Ephesians 6:5-9

" Slaves, obey your earthly masters with respect and fear, and with sincerity of heart, just as you would obey Christ " However, the next paragraph stating " And masters, treat your slaves in the same way. Do not threaten them, since you know that he who is both their Master and yours is in heaven, and there is no favoritism with him. " that part would be removed. So the Christianity as you may understand it as today, was not even the religion they were being taught but rather a co-opted or corrupted version whose only purpose was to make good obedient slaves to serve white supremacist institution, which is no surprise largely rejected when people had another option.

As for the amount of nativeness to the continent, I mean I'm not sure if that was the measure or not. There are arguments on both sides. Jesus is said to have lived in Egypt; the Ethiopian and surrounding Christian states of ancient are among the oldest Christians in the world (older than any branch except the Armenians and Syrians) and much older than Islam. But much older than anything in Europe in that regard. Although I believe it is said that Muhammad or his followers hid out in Ethiopia for some time as well.

Further, it is complicated by the history of South Arabia being controlled by and populated by a significant number of Ethiopian/African people right before the rise of Islam. This is something still hotly contested by scholars in Islam, so I won't take sides on this, but there is a group of scholars who believe Muhammad was descendant of Ethiopian peoples living in Arabia due to its control over the southern part of Arabia. So the theory goes while technically not in Africa the religion has its roots in an African race of people living in Asia. They bolster this point by pointing to the semitic origins the arabic language and semitic languages falling into the afro-asiatic language grouping of African descendant languages spoken in asia.

Part 1

Islam has a claim to, or at least appearance of, universality and to some appears non-racial. Of course, Muslim is not a race (I wish I did not have to include this) but confessional identity in Islam is believed to supersede ethnic or racial considerations. For this reason, Islam can be seen as appealing to people such as black Americans especially during first half of the twentieth century. The often cited anecdote of Malcom X is his hajj to Mecca where he encountered a variety of people worshipping together in unity, which apparently affirmed his commitment to Islam.

The reality of ethnicity within Islam is much more complicated of course, and Muslims are just as divided internally as Christians. Sunny and Shiite are the most well known broad sects, but there are groups within this division. Arabs alone are extremely tribal which is something that persists to this day. Present day Arab monarchs often have to diffuse disagreements among tribes and clans that could lead to civil war and violence. Turks often do not like being grouped in with Arabs or other Muslim majority ethnic groups because of the Turkic heritage as a military elite throughout the Islamic world. The Ottoman Empire was also not really a "Turkish" led empire, because identities became mixed and Ottomans themselves had clear distinctions between (for example) Bosnian, Serbian, or even Italian origin people within the elite. However, as another poster alluded to, the particular type of Islam that was common among black liberation activists is one that is unique to the United States. These groups also advance a theology that is not consistent with traditional schools of Islamic jurisprudence.