That's because he's technically not a Transformer. Back then the Gobots property wasn't part of the Transformers Brand.
In America it was owned by Tonka, and it was based off of a line of transforming Robots from Popy, a then subsidiary of Bandai.
It wasn't until 1991 that Hasbro bought out Tonka and all its intellectual properties including the Gobots.
This guy is Road Ranger, a Gobot Guardian. (Not all red and blue trucks are immediately Prime)
http://www.tfu.info/Gobots/Guardians/Ro ... ranger.htmI actually had him as a kid, and he was my replacement Optimus Prime as I was never able to get an actual Optimus as a kid.
He's got some diecast in the cab, and he is pretty cool.