The GRE is designed to reward hard workers as well as intelligent people, that's why it is a widely used metric. Grad schools need hard working people as much as (probably more than, to be fair) they need intelligent people.

I am joining a CS PhD program in an US university this fall. The GRE, especially the math part, is high school mathematics. If you are not good at math, you can ace it by studying hard for a month.

That is why a low GRE quant score reflects that you haven't really bothered.