User blog comment:MisterWoodhouse/The first migrations to the Unified Community Platform/@comment-172.58.221.146-20201229185533/@comment-1038387-20201230000814

This is a simplified version of my understanding,which is probably partially incorrect. Under the surface, thread replies are all independent pages, linked to the original. All comments are subpages of talk pages. All of those are transcluded on the page. This isn't even deep under the surface; it becomes obvious when a category is added to one, or a red link or nonexistent file. Blog replies have pagination, but threads and comments don't, which impacts the server drain on larger chains. Try opening a forum thread with ~500 replies, takes ages to load fully.