The people who work on the ActivityPub specs are humans and we use the Fediverse. We're not space creatures or robots. We care about other humans and we love our kids and dogs.
There are currently two specs being worked on for reply control. You'll probably see some more work on this coming out soon.
Did we think of everything when we created ActivityPub? No. Did we make it extensible so future people could improve it? Yes we did.