A commoner—if brave and honest—can become a squire, and someone who performs a feat can earn the title of a knight. But the knight also accepts additional responsibilities: to honor women, protect orphans, fight the forces of Darkness, not yield to sorcerers and dark magicians.
And besides, knights are often forced to travel—some by their own oaths, some by hunting for church relics, some by searching for worthy opponents, and some by carrying out special orders of the king.
Or—of the queen.