Because they don’t get listed by browse.feddit.de you’ll want to browse https://kbin.social/magazines to browse “magazines”, which is what they call communities
e.g. !RedditMigration@kbin.social
or directly, https://kbin.social/m/RedditMigration
Why YSK: Federation literally just synched up thanks to the tireless efforts by @ernest@kbin.social over the past few days.
Lemmy instances don’t pull content (and make the link work) until someone searches for the relevant community.