Because the supply of BCV is smaller, and/or the demand is higher.
For some, only BCV will do. If that's true for you, then pay the extra so that you can stay where you really want to stay. Personally I would buy at BWV and laugh all the way to the bank. SAB is nice, but it's not *that* nice. BCV's dues are also a smidge lower, and that may make up for it, but I haven't done the math to check. I suspect the difference in price swamps the difference in dues under most reasonable time-value-of-money assumptions.