More precisely, where Red Hat-initiated projects use CLAs (or, in the odd case of Cygwin, copyright assignment), it is for historical reasons. The substantial numbers of Red Hat-initiated projects that do not use CLAs might be said not to do so for historical reasons too, but the avoidance of contributor agreements for new Red Hat-initiated projects from ~ mid-2008 to the present was deliberate, and indeed was deeply influenced by adverse community reaction to Canonical's use (as was) of copyright assignment.