The same reason prophet Jesus still has followers and same reason prophet Moses still has followers; Peace be upon them all. Refer to questions below for more information.
Addition:
All three religions stem from the same source - the Yahweh (YHWH, Jehovah) of the Jews.
Christianity added Yeshua (Jesus) and the Holy Spirit in an awkward compromise trilogy.
Islam was a purified version with the god, in Arabic called Allah, with the war leader and visionary Muhammad as the principal prophet, but the prophets of the other two religions (including Moses and Jesus) also recognised.
They all continue to exist in parallel today.
no
Prophet Muhammad Born After Christ / Isa. So he didn't exist in 620bc
what did muhammads followers think of him? Followers of Prophet Muhammad (PBUH) regard him as the last messenger of god, and the servant of god. Prophet Muhammad (PBUH) is the idol of all muslims, he is the leader.
Prophet Muhammad (peace be upon him) didn't try to find solutions on his own. He is a God prophet who is inspired by as what he has to do and not to do, Qur'an was revealed to the prophet by God where prophet Muhammad and his followers get all Islam teachings and rules in addition to the prophet teachings (Sunnah).
Prophet Muhammad PBUH laid foundation of Islamic Rule in Madina .
It was not by prophet Muhammad (PBUH) choice but per God (Allah in Arabic) command to him. It was to honor prophet Muhammad, to confirm support to him, and to strengthen the faith of his followers. refer to related question below.
Never heard about any conflict between prophet Muhammad (peace be upon him) and the Muslims (his followers).
The effect of the teachings of the prophet Muhammad was people still believe on his teachings....!!
No, Christianity may have marginal more followers (if valid) but not twice as Islam followers per Quran revelation to prophet Muhammad (PBUH).
Islam religion per God Quran revelation to prophet Muhammad is founded by Allah (God in English and same God in Christianity and Judaism) and not prophet Muhammad (peace be upon him). Prophet Muhammad is the God Messenger and prophet who conveyed God message to his followers. Refer to related question below
Muhammad never wrote the Qur'an down. He recited it and it was memorized by his followers. It was transcribed after he died in the mid-7th century.
The Honorable Prophet Muhammad (peace and blessings be upon him).