I haven't ever washed a belt and my BB is slowly fraying. Mine is from ordinary wear and tear but I do know of people rubbing their belts to get the frayed look.
Poseurs gotta pose...
In my experience, practitioners of Korean arts seem to replace their belts before they get that faded, frayed look. There are exceptions, of course (GM LEE, Kyu Hyung, for example) but as a rule you don't see "old" looking uniforms, including the belt.