Because he’s a pirate. It’s part of his design.
@Bob1hello know I'm pretty sure the damage wasn't an intentional part of his design. His exposed exoskeleton would surely ruin the immersion for all the little 8 year olds at Freddy Fazbear's
Because Scott modelled him while in a car. It's literally stated in the blurred text from 3's newspapers. That's all there is to it- but if you really want an in-universe answer it's cause he's out of order so likely rotted from disuse.
I agree with this