Well, number one, he isn't a shooting guard, he is a point guard playing small forward. Secondly, that should tell people just how good this guy is, the fact that he doesn't shoot the ball very well, yet 9games into the year, he is averaging 16.3 points per game. As was also noted, Briscoe usually draws the assignment of the best guard of the other team.
Not in reference to the quoted post, but to this thread in general, there is more to basketball than shooting. However, for whatever reason, people seem to think shooting fixes everything. It can masks some things, but over time, even those things come to light. As has been said before, Cal values defense over everything else. And to be honest, basketball is more complex than most are giving it credit for. Just because Mulder does a decent job guarding his man when he is in there, doesn't mean he is adequate at playing it. If he plays for Briscoe, then it is likely that Fox now has to switch to guard the guy Briscoe was guarding, then Monk has to switch to the guy that Fox was guarding so as to give Mulder the weakest of the perimeter players. Meaning that you didn't just get worse at Mulder's position, but actually 3 different positions. Then Mulder does an adequate job on his man and many people claim he isn't as bad as it was claimed to be. Yes he is just as bad, but it is being masked.
Cal plays the regular season for 2 reasons, seeding and preparation for the NCAA Tournament. Fans live game to game, but Cal does not. Most of Cal's decisions revolve around those two things.