Plot hole: Reed's plan to teleport the planet away is based on the upscaling of the teleportation device he invented a couple of days prior. Every time he uses it, though, it uses TWO pads: a transmitter and a receiver. It takes the collaboration (and the power grid) of the whole planet to use the transmitter, but the receiver is conveniently absent. It would have invalidated the whole plan.
Answer: Possibly because it was the closest building with height to it as they are about to be hit by a gigantic wave of water. There was no snow yet, so I don't believe burning books or snow was on anybody's mind yet. It turned out to be a great idea as snow soon starts to fall and those books were literally a life saver.
Susan D. Santos