Actually on Funny Cars and Dragsters, it's for weight and for ease of inspection for cracks and repair. Pro Stock and most everyone else are painted or powder. I prefer paint for ease of fixing and/or adding stuff (welding) and then fixing the finish. Plus guys are still concerned with appearances.

NHRA hasn't allowed plating (chrome) on cage components for years. Paint and powder only.

If the results don't match the theory, change the theory.