Is there a reason why Sanctuary Onslaught doesn’t have Murmur enemies?

I’ve been affinity farming to raise my MR, and I was noticing that in it, we have, Grineer, Corpus, Infested, and the Corrupted. But we don’t have any of the Murmur or other newer factions. It made me wonder: Is there an in lore reason why? Does Simaris just not know? Does he know and just not care?