alt Hacker NewsBluesky is political because their invite-only on-boarding process for months meant that only really tight knit subgroups and subcultures found their way in. By the time your average person who just wanted to stop seeing ads about Great Replacement Theory or whatever found their way into Bluesky, it was chock full of furry art, "fandom" posting from teenagers on the spectrum, and political rambling from people who haven't touched grass since puberty.
How does having a really tightly controlled and/or lengthy invite period translate into the user base being of one particular political viewpoint? I'm not seeing the causal link. Even if I take at face value your claim that "only really tight knit subgroups and subcultures found their way in," I still don't see how these subgroups or subcultures would necessarily have the same political views.