The enigma of Bryan (and others)

Bryan has been playing bridge longer than I have. He's a more rigorous bidder, a quicker-thinking declarer, and all in all I believe a better player than I am. When I set up the running score tally nine months ago, I didn't have any particular expectations; but it has revealed a mystery. My score has steadily pulled ahead by miles, while Bryan's has lingered very close to zero for months and months.

(I'm taking Bryan as an example, but the low scores of others puzzle me equally.)

With no false modesty, I'm quite sure that I'm not the best player of our crew, and certainly not by such a margin. (Nor do I falsify the scores.) I am probably the best memorizer of conventions, but that doesn't confer a great advantage with a series of randomly rotating partners. The main difference in style between Bryan and I is Bryan's requirement of a sound 13 points to overcall, while I'll jump in with 9 good points if I think it'll do any good. And I'm perhaps more eager to shoot for slam than most people; I suppose that could be a factor.

Any theories?