It should be noted that cosocial has 10 registered users according to their front-page. Small instances frequently make idiosyncratic federation decisions and exactly because they're small they have little impact on the overall health of the network.
Beehaw's defederation as a "load-bearing" instance in the lemmyverse that is already entangled via cross-instance subscriptions is much more damaging and degrades service for like an aggregate 50% of the lemmyverse.
I wouldn't sweat this cosocial thing, it will probably never impact you in a perceivable way.