Because the stroke needs to go onto a layer that’s getting shattered. What I’m doing is animating the end point of a stroked circle to match a rotating particle emitter so it looks like a hole is being cut into the layer from behind, and then blowing the whole thing up with shatter.
I guess that I could just move layers into a new comp, generate the stroke on its own layer like you said, add the glow, and then place that comp into the main comp and shatter it there. Does that sound like the best option?