Because American wagyu is a wanna be product( at least the stuff I’ve run across) raising wagyu beef is about the way they are fed as well the type of care they receive as much or possibly more than the genetics.

so the burger thing is three fold,

number1: trying to capture some more value with the rest of the animal that has at best base value, wagyu or not. 

number2: beings the USA doesn’t have “true” wagyu, it gives the butcher a way to utilize steaks that don’t meet the low standards that our country considers wagyu, pretty hard to tell what it is supposed to be when all ground up.

number3: gateway product, lower price product that’ll get people with a few extra bucks to try, so brand and product identity will be established (hopefully), and result in repeat sales of higher margined product.