Megatron didn't take the form of any human-made vehicle throughout the Transformers movie series until DTOM. He apparently despises Earth and humans so much that he refuses to take the form of
Megatron Transformers: Revenge ... | Statue | Prime 1 Studio
How did Megatron go from being Galvatron back to being Megatron again with a different form in Transformers: The Last Knight? - Quora
Transformers Age of Extinction Statue Galvatron EX Version 77 cm – Animegami Store (EU)
Megatron 1:4 Statue of Transformers movies by Kami-Arts
Megatron | Transformers Film Series Wiki | Fandom
Transformers 4 Fan Made Clip: Megatron consults Unicron - YouTube
Transformers 4's Worst Villain Raised an Important Spiritual Question