Why are we 'milking' crabs for a coronavirus vaccine?

This isn't specifically for coronavirus, from wikipedia

> Amebocytes from the blood of L. polyphemus are used to make Limulus amebocyte lysate (LAL), which is used for the detection of bacterial endotoxins in medical applications.

There's a nice video here on it (3:22) https://www.youtube.com/watch?v=LgQZWSlLBnA