Why are holes needed for the finer grating of cheese?

So a cheese grater is usually ported. For Romano cheese I just take a serrated knife and sort of sand the top layer off with the serration pointed straight down onto the cheese. That makes a nice effect.

So why are the finer sides of cheese graters not more like files?

Here are my thoughts on why a cheese file isn’t common: the cheese would clump up (I find it does on those tiny little punches anyway), it is more cost effective to make piercings in the metal that jut out tiny barbs than to make a surface that is molded like a file (the tiny holes are unintended)...

Thoughts?