@dilettante look no further than our about page to find two others listed as sibling instances! And then there's blacktwitter.io and terror.black, and that's just off the top of my head.
It's not like we don't exist, or even that we are all minuscule servers. Blacktwitter.io has 100+ active users, which ain't huge but it ain't tiny either.
Now, I'm going to answer your question with another question:
What has Mastodon (or hell, any of the other fedi platforms out there or shit even ActivityPub itself) done to make the fediverse safer for Black folks? What actions have they taken to court Black users for decentralized social media or protect us from the white supremacy they know is common on the internet?
How many Black folks do you see on the mod teams of the biggest instances out there?
And before you answer, keep in mind that pledging to actively moderate racism doesn't mean shit when the chips are down. I can tell you that from experience. I need tangible actions.