But hardly anyone in the Fediverse, next to no-one on Mastodon and literally no-one outside the Fediverse knows that Misskey exists. Not outside of Japan anyway. Or any of the Forkeys, for that matter (if you’re a Westerner and neither an otaku nor a weeb, Iceshrimp or Sharkey may suit you better).
For more Mastodon users than not, the Fediverse = Mastodon. And outside the Fediverse, hardly anyone has even heard of the Fediverse.