There are a lot of holes in all cars that aren't used, and it seems extra odd with vehile specific parts. The ony guess I can come up with is that it's cheaper to drill the holes than leave them out.
Here's an example: I got one of the last GM NOS radiator supports. It has a bunch of extra holes my original does not.
But then I had to drill out the 3 holes for the voltage regulator to the correct size and provide a new 2nd hole for the horn relay pin.
2012 Mustang Boss 302 #1918, Competition Orange. FGF replacement 2006 Mustang V6 Pony, Vista Blue. Factory ordered. 2019 BMW X3 (Titled to the wife, but I'm always driving it for her. So I'm claiming it) Old projects, gone but not forgotten: 1967 FB 400, original CA car. After 22 years of work, trashed by the guy who was supposed to paint it. I had to sell it. 1980 Turbo Trans Am 1970 Mustang fastback, 351C 4Bbl, auto 1988 Mustang GT, 5 speed 1983 F-150 4x4, built 302 1994 Chevy K2500 HD 4x4, 454 TBI