@randahl @kypeli It can be seen as a bit annoying but it is not that big of an issue.
If you are the author you'll see all comments to your posts. Also you see all comments if they are made by your contacts (regardless to whom) and all comments made from/to your instance. This is why users of huge instances rarely notice it. Also you'll see comments your contacts already interacted with.
This adds additional value to boosting/resharing - you literally provide visibility to the content you consider valuable. Also it helps to reduce spam and toxicity - everyone can run their instance and join the network but if a spammer or a troll from malicious instance starts leaving comments on Randahl posts for example they won't immediately spread to the entire audience. However someone interesting will get reach because people will interact and create more and more visibility.
Also it has technical benefits - some instances are small, some are private. To see all comments everywhere they'd have to federate everything which would create a lot of load and be very expensive.
I am not saying it is perfect but it is another way and it has some benefits too.