Those examples are all forms of linking back to the content which is still hosted by the original server in which it was posted. Effectively they are sharing links to the content over the content itself, because if the hosting server removes the content then it is no longer available through those other mediums. And yes there are caching mechanisms involved, but those fall to the personal use case because the cache is not made publicly available.

For these bridge services to work, they are creating and hosting duplicates of the content. That is the biggest difference. If BlueSky actually federated then they would not be rehosting the content either.