Why? "Because his armor looks kind of like a Titans because its made of metal and heavy looking and stuff". Yeah I answered that for you. Now I'll give my answer, to which no Titan has been able to refute. Master Chief is a Hunter in personality and physical attributes, the main reason for his strength is the armor he wears, his speed however ranged from 70-80 MPH. He is quick and agile, smart and able to figure his way out of tight situations. He's quiet and a lone wolf. So he has all of that in common with Hunters. That's why.