Why the Darn Heck Don't Metronomes Yield Tachyon Fragments

I think theres 4 or 5 different artifacts that yield shipping rate fragments. What I cant figure out is why salvaging a metronome, which increases hatchery rates, ends up giving you shipping rate gems, instead of egg laying and hatchery ones.

Pretty sure the only artifact line that salvages into tachyon are the co-op egg laying artifacts, right?

However months later and this fact still bugs the dang heck out of me.