I guess it begs the question why is the contract not more split up into different regions so that 95% of the country doesnt have to wait and wait and wait for the other 5%?
Bargaining under a single National Master Agreement gives us more leverage at the table and (in theory) keeps the company from trying to pit local against local. The threat of 250,000 Teamsters going on strike is much greater than, say, 10,000. That leverage is why we have National Master Agreements.
That being said, each region/local has their own set of issues and needs some measure of autonomy. The only way to get the locals to agree to a Master Agreement was to allow them some level of control locally, hence why we have the supplemental agreements and riders. The Master Agreements, per the IBT constitution, cannot be fully ratified until all supplements and riders are passed.