"One hundred billion trillion planets in the cosmos. You want to know, don't you, why they keep coming here?" Anthony Hopkins, TF5 The problem in that statement is that Earth has never really needed a relevant reason to be a battlefield. It was just a matter of the Decepticons coming across another world to plunder resources, and the Autobots fighting against them to protect the lives the world carries (for friendship or for justice). It's a situation that keeps coming up in recent TF features: - Unicron is the Earth in PRIME - all five of the Bayformer films have had some conspiracy that ties the Transformers to Earth (Megatron stored and studied, the Matrix of Leadership hidden, Apollo and the Ark, Quintessons annihilating dinosaurs, a medieval era Transformer) - TFA redid the 2007 film's angle with Megatron and Sari being part Cybertronian It's an inherent problem too, because there needs to be a reason to keep the Transformers on Earth and to keep humanity relevant, otherwise people (fans and non-fans) will lose interest. It's also why most Transformers have to be disguised as Earth vehicles instead of having alien modes, or why humanity needs a major role in a TF feature. It's a difficult situation that may not be easily resolved. Ideally, I'd like to see the war take place across different worlds (including Earth) which could lend greater variety of environments and Transformers. Cybertron did something like this which worked out fairly well. But then I'm speaking for myself, and I'm not sure others would like this concept.