Because they like him and because he is their role model.
He is the prophet of Islam. The Muslims are ordained by Almighty Allah to follow him. You can't follow a person sincerely if you have no respect for him. The Muslims not only respect him they also love him more than their own life.
Muslims say "peace be upon him" when mentioning the Prophet Muhammad as a sign of respect and reverence. It is a way to invoke blessings and show honor towards him.
there are more than one million Muslims named Muhammad.
Muslims love and revere Prophet Muhammad, God bless him and grant him peace.
Muhammad
Muhammad did
Muhammad, undoubtedly.
Muhammad's followers where called muslims
Muhammad peace be upon him
Because Muslims love the Prophet Muhammad (peace and blessings of Allah be upon him).
Muhammad
Sunni Muslims.
Never heard about any conflict between prophet Muhammad (peace be upon him) and the Muslims (his followers).