So in simpler terms maybe, there needs to be a trigger for federation to occur. Instances don’t ping other instances automatically. The simplest trigger is to go on an instance’s post from your instance and post a comment there.

It’s like there’s no radar and you need to actually see the plane in the sky with your own eyes.

Another way of encountering an instance would be if you both federate with a third instance and they post there and you see it or interact with their post I guess.