Because Muhammad claimed to be an Abrahamic Prophet of God. But the members of the Abrahamic religions of Judaism and Christianity rejected Muhammad as one of their Prophets of God.
In fact, Muhammad claimed to be the LAST Abrahamic Prophet of God.
And while many Christians and Jews have converted from their religion to the cult of Islam, there are countless millions of Muslims who converted from being alive to being savagely murdered dead in the name of Muhammad.
It's not about Islam.
It's about proven liar, rapist, slave owner, thief, killer Muhammad!
You don't know much about Muhammad, do you?