This thread title should be changed to "Why don't I get upgraded IAD-SFO" or just merged with one of the myriad of threads already going about hub-to-hub upgrades being non-existent for elites.
OP is wrong to assume they are 76th on the list. Not all 50 business class flyers are elites who were above the OP's status. Many of them are lower level elites or just not elite at all and their company booked them on United.
-RM