Majors sell their own tickets. Regionals are effectively subcontractors. The majors therefore control their own destinies. This generally leads to better pay and work rules. A subcontractor will never have better pay and work rules than the prime, you can't compete on price with the guy who is hiring you b/c you are less expensive than his own operation (unless you provide something they need that they don't have, doesn't apply to airlines in the regional jet realm right now). As legacy carriers shift to international focus and subcontracting domestic capacity to "regionals", the gap between a regional pilot and a domestic mainline pilot will narrow. Unfortunately, it'll probably work opposite the way we'd prefer. Mainline domestic pay will come down as they play their labor forces against the threat of domestic outsourcing.
Of course this all changes if the mainlines decide to take back the "regional" capacity.