Because it seems odd that the Decepticons had been planning things since the 60's on Earth even though they both seemed like they'd never heard of Earth before they arrived in the first movie. Also, I guess Shockwave was heading up the plans with the humans in the 60's since Megatron was frozen in the Hoover Dam (although he still really acted like it was all his plan in this film.)

Also, I thought they really missed an opportunity for a great opening scene. I think it would have been better to establish that the Earth now had better defense planning to prevent the Decepticons from flying in (hence the reason they needed the pillar bridge to get to Earth to attack it). I would have preferred a bad ass battle scene in the beginning with the humans/autobots having an upper hand, forcing a Starscream led attack from landing on Earth (but maybe a couple sneak onto Earth to help put the Moon plan into action). Save the heavy moon landing exposition to a bit later.

That would have been much better than the completely random Middle East attack scene they threw in there.

Also, I think internal beef between Megatron and Shockwave (who should have been implementing the Earth plan) and Sentinel would have made those characters stronger and not forced them to rely on the corny, out of the blue mindfuckery of Megatron by Carly in the flick.