Originally Posted by jsloan

It's because upgrades on that route are nearly impossible for anyone, especially on a Friday. It's not possible to know how many GS are taking the flight (except by watching during pre-boarding -- but, even then, not all GS members choose to pre-board). However, if you purchase in advance, business class is typically $300 more than coach. Paid tickets end up being very popular, which is why upgrades are quite rare.