@hmans Could be that they are lazy fetching it or something
I was quite amazed to see issues like this be totally left to the implementers of #ActivityPub
Especially as #PubSubHubbub / #WebSub which #OStatus and other predecessors use (and the #IndieWeb still use) was specifically designed to avoid thundering herd problems that arise from a lot of subscribers all eagerly fetching content at once upon receiving a ping about new content