On the topic of Twiter, Mastodon, and the Fediverse, why do federated FOSS alternatives to popular platforms not offer a read-only version of said platform as one of its instances to augment its lack of content?

In the example of Twitter, Nitter already exists as an alternative front-end. Now what if there's a Mastodon instance that uses Nitter to wrap official Twitter content and serve it as if it where the twitter.com mastodon instance? Again it would need to be a read-only version as Twitter is not Mastodon but it would help fill the content gap for sure.

Now Mastodon might not have a content issue but PeerTube for example very well has and in that case masquerading YouTube as a PeerTube instance would become very interesting.