Ummm.. Earth IS a disaster magnet all on it's own. And when you said that, all I can think is; INVADER ZIM!
Because it wouldn't be Live Action for a movie to be made about Giant Effing Robots fighting on Jupiter, with no humans. jD001
so i guess then Spoiler Sentinel was with the Fallen as well, as he might have known about the harvester, or did he get that info from Megatron?
The Harvester is designed to refuel the Allspark. Considering the Allspark's semi-mystical energy-based motives and standing, it's not unfathomable that it would seek out the harvester. Actually it is.
Spoiler Megatron probably suggested earth for this whole reason. If they could bring Cybertron to the earth and activate the harvester somehow it;d be easier to re power Cybertron.
Maybe it was because Earth was so full of other resources they chose us.Not only do we have a large sun,we have a large amount of natural energy sources.