The newly formed (since Transformers: Age of Extinction) Transformers writers room teamed with Hasbro to put together a sprawling lore that covers a massive history that draws from the cartoons and comics, uniting the mythologies into a single Transformers “bible.”
This changes with The Last Knight.
Each movie has merely been tacked on without any major over-arching themes to tie everything together.
Michael Bay originally expected Transformers: Age of Extinction to be his last movie for the franchise, but after seeing the work done by the writers room, he decided to do one more.