Because BCCG is not one of the main grading companies. They are some off shot of someone else I think. BGS, PSA/DNA, SGC will always sell for more then the others!
It's the Collectors Club grading of Beckett. I use the term grading loosely. It' rare to find anything but a BCCG 10 - they do exist but they are like hens teeth!
I wouldn't buy them; however they do sell for pretty cheap so sometimes it might be fun to buy some of them, crack em and see how well they really grade by a proper grading company.
Ones I'd stick to are (in no particular order): BGS, PSA, SGC and GAI.
BCCG are for amatuers !!!!! The premiums for a good grade are generally very much smaller than the more established joints such as BGS or PSA. Cheers Alex