Why? What possible motivation is there for someone to lie? Nobody on the plane had to call SFO to get the information about connecting gates. It's available to each flight attendant using their handheld app. And in post #12, Lux Flyer claims that the gate agent -- presumably the other gate agent, not the one you talked to -- actually did call to see if the flight could be held, and was told no.

Do you think the pilot just wanted to enjoy the view? Or maybe he was a bad apple trying to make UA pay for a bunch of hotel rooms? Or just a sociopath who thought it would be fun to inconvenience an entire planeful of passengers?

Not every gate at SFO can accept a widebody plane. And even if an alternate gate were available, it wouldn't necessarily follow that an alternate ramp crew, gate agent, etc. were also available.

Huh? You weren't waiting to let some other plane unload first. You were waiting for another plane to depart. Or, if you're just saying, "why didn't they prioritize my flight over all other flights for some alternate gate," see the previous point.

Except that it really could be, and in fact it fits what you describe quite well (except that the gate agent could have just said that). The rest of it though -- pulling away from the gate and then stopping to finish paperwork? That's absolutely in line with the idea of someone nearing the end of their duty day. The airline needed to make a decision whether to offload you all or not, because not only might someone else on standby already have taken your seats, but they also needed to know how much fuel to load and whether or not the weight and balance checked out. Closing the door and pushing back from the gate ensures that the flight gets logged as an on-time departure and the cabin crew gets paid; waiting to complete the calculations can then allow them to make their wheels-up time that would allow them to land prior to hitting their flight duty limits. While you may be thinking that another minute or two might not make a difference, or since the plane was just sitting there, they should have let you on -- a minute or two really could make a difference, because if they miss wheels-up they may have to wait behind on-time traffic; and they may have to throw out all of their calculations and start from scratch, or even take on additional fuel, in order to accommodate 15+ additional passengers that they didn't think were going to make it. The three additional minutes it would have taken to allow you on the plane really could have meant a time-out and cancellation. (And, unless you checked the seat map and saw a bunch of empty seats -- there probably were standby passengers for SFO-EWR. And since you were traveling up front -- I can just about guarantee your seats had been given to upgraders when you failed to appear -- so if you'd have gotten on board, at best you were looking at middle seats in the back of the plane).