I can see deleting some of this data is probably non-trivial too, given that if you want to keep the data consistent you have to recursively follow all the relationships between objects and delete related objects too. For example, delete a post, and you have to recursively fetch all comments and delete those, and then all replies to comments, etc.
It's definitely doable and if they're not currently doing that because they choose not to for sure, though deletion of highly-relational data like this is an interesting problem, idk I wanted to bring it up (: