Transformers (2007)

Continuity mistake: When Sam and Mikaela handcuff all the agents, Sam is wearing a black short-sleeved tee shirt atop a blue long-sleeved tee, before putting on the hoodie. We see the dark tee sticking out when he and Mikaela climb onto Prime. Then moments later, Sam is wearing ONLY a long white short-sleeved (we see it has short sleeves when Bumblebee gives him the All Spark later, through a tear in the hoodie sleeve) tee shirt under his hoodie, when he falls from Prime, when he witnesses Bumblebee's capture and thereafter. (Earlier, after he knocks Mikaela off the moped, from that point on there is a very large hole at the back of his blue and black tees, where we see his skin under the jagged material edges, with no white material seen anywhere. We also see no sign of a long white undershirt at any time when Sam's dark tees go up, during his many action shots.)

Super Grover

Optimus Prime: With the All Spark gone, we cannot return life to our planet. And fate has yielded its reward: a new world to call home. We live among its people now, hiding in plain sight, but watching over them in secret, waiting, protecting. I have witnessed their capacity for courage, and though we are worlds apart, like us, there's more to them than meets the eye. I am Optimus Prime, and I send this message to any surviving Autobots taking refuge among the stars. We are here. We are waiting.

Trivia: There is an extra scene mid-way through the credits.

Question: Can someone please explain why all this happened more than 100 years after Megatron crash landed on Earth? Why didn't the Transformers come sooner?