Here's how starter packs really work:
Suppose you stayed on Twitter because you ran a local model airplane club, and your club met and chatted and DM'd there. The club had 80 members.
30 moved to BlueSky, but most of the convos are still on Twitter
You make a starter pack called "[town name] model airplane club." You put the 30 who moved to BlueSky in it. The starter pack is now attached to your account. It makes it easier for the other 50 people to join BlueSky.