BlueSky users skew younger than Mastodon. Again, in large part because Black Americans are young, and white Americans are old.
The most common age for a Black person in the US is 27. For white people, it's 58. A place with no Black folks tends to be older.
This is why white people trick themselves every year into thinking that young voters are less racist. No. Young voters have more Black people. Every generation of white folks votes pretty much the same.