A neutron star "merger" is a collision between two of the hottest, densest objects in the universe that are still objects. These collisions are incredibly messy

A neutron star "merger" is a collision between two of the hottest, densest objects in the universe that are still objects. These collisions are incredibly messy and energetic. Stuff gets blown everywhere - a lot of stuff. Once freed and blown out into space, the remaining neutronium is incredibly unstable without the intense gravitational pressures holding it together. It will rapidly decay into relatively stable material.