I would guess that it's for the same reason that "Italy" is spelled as such in this country and not "Italia" (and that, e.g., Germany is spelled Germany and not Deutschland).

Also, evidently "Ciocc" was either a regional variant spelling or, more likely, simply made up by someone at the bike company who had never seen the word in its spelled-out form (checked, and the, or at least one, correct Italian spelling is "ciuccio").