I think the advantage that federation provides is that there is no central trove of data you can easily access. With commercial platforms like Twitter or Reddit, all the data happens to be in one place under a single jurisdiction. However, the nature of the Fediverse is such that it’s a bunch of different servers scattered across the globe. Collecting data effectively means having to make deals with each server operator on case by case basis, and governments can only coerce servers that happen to be in their jurisdiction.