Mbin has at similar approach where it is possible to see the number of comments on other communities:

This issue is due to Lemmy.
The Lemmy devs recently stated that this is a client problem, and that they don't plan to change that
In lemmy-ui we’ve chosen to link the posts at the top rather than combine comment threads.
https://lemmy.dbzer0.com/post/46984024/19528869
And if everyone was using piefed that merges cross posts, this war against instances makes even less sense.
Instances still have different moderation policies. A comment could get on banned on one instance and allowed on another. Being able to see them all doesn't change that.