Answer: Because of the connection between religions.
Step-by-step explanation:
The mentioned religions are characterized by monotheism, and these are the three largest monotheistic religions in the world. When we talk about the mass acceptance of Islam in the Arab world, it is necessary to consider the holy book of Muslims, the Koran. The Qur'an states that the Torah (the holy book of the Jews) and the Bible (the holy book of the Christians) are also a divine work, but that they have undergone changes over time. On the other hand, the same god offered the Qur'an to the people, and the Qur'an itself states that it will remain unchanged.
Also, the emergence of Islam is related to the early Middle Ages, and the church did not send missionaries to Arabia on a larger scale, so people accepted Islam and rejected the ancient pagan beliefs. When we talk about the spread of Islam in Africa, it is a consequence of historical currents. Islam in Africa spread through Arab traders but also missionaries. People accepted Islam because of the dogmas that religion dictates; the teachings differed from what the previous religions offered. These are the main elements of the rapid popularization of Islam in these parts of the world.