It's all because Hasbro made the robot mode cutting of the windshield too big and squared off at the bottom. If they had made the cutting smaller and more rounded, it would look a lot better.Normally I'm not bothered by toon-style decos just having sky blue painted windows but no, I don't like that.
Here is a crude illustration showing what I mean, with the official cutting on the left and my suggestion on the right: