Intuitively, once you have the idea that some DNA is responsible for turning on and off the DNA that codes for proteins, it's possible to imagine that the regulatory DNA is actually the most important part. In the ingredients list of a recipe, you might think the coding DNA gives you the list of ingredients, but the regulatory DNA gives you the amounts of each one, plus the order in which you add them to the bowl. If that's true, then different variants of regulatory DNA should be selected for and against, and evolutionary molecular biologists ought to be tracking those variants like they track alleles of genes. But evolution always is discussed as if it's just about different gene frequencies.
Is "regulatory evolution" a thing? If so, is there an understanding of how big a thing it is? Or, if not, why not?