Granted this had to do with the fact that unlike any other agreed upon standard protocol, Reddit posts are not accessible except by indirect means, i.e. you can’t download the contents of a community the same way you would with a git repository or an email server and migrate it elsewhere.
Tangentially, https://old.reddit.com/r/DataHoarder/comments/12ucc9z/downlo... and https://old.reddit.com/r/redditdev/comments/c93rdt/how_do_i_...
A sibling comment mentions ArchiveTeam, which ends up in the Wayback Machine. Some work to be done around tools to make that corpus more readily available for consumption and perhaps backfill. Lots of existing tooling to query the Internet Archive's CDX servers to understand what coverage looks like and retrieve archived content.
They could probably import the data to lemmy.