Most likely because Megatron pretty much took over his ship when he came aboard. chuckle (Sorry, I can't draw giant robots...you'll have to live with seeing the human avatars.... XD)

Transformers belongs to Hasbro. :)
Rodimus human avatar belongs to IDW Publishing and whoever came up with the idea there. Please go read the "Transformers: More Than Meets the Eye" comic if you enjoy weirdness and adventure in the TF universe! :D