Let’s get this out of the way first: no one is slurping down a cup of live, wriggling larvae like some kind of protein shake. The term "maggot milkshake" is a nickname for a liquid suspension of sterilized maggot secretions. Scientists extract the excretions and secretions—basically the goo and digestive juices they produce—and mix them into a solution.
It sounds icky, sure, but think of it like this: you wouldn’t say you’re drinking a honeybee when you enjoy a spoonful of honey, right? Same idea here. We’re after the superpowers these little guys produce, not the bugs themselves.