Originally Posted by
seenitall
Given that this was a 737-900, my guess is that there was a mistake in loading the cargo holds -- and stuff that was supposed to be put in the back hold was put into the front hold. As a result, they had a choice: either wait while cargo was taken out of the front hold and put into the back one, or tell the PAX that they had to move back. Given that doing the first choice would cost UA time and money, you can guess which option they chose.
The thing with that though, is with how tail tipping prone the 739 is, it's standard procedure to load the majority of weight into the front. Because when it reaches its destination, the tanks are almost empty, and all the pax are getting from the front first...having cargo weight in the back will make it drop real quick.
So I could see it making sense to have pax move back for takeoff to get the balance, but then come back forward for landing to avoid the tail tipping issue.