This, of course, isn't new. I once worked at a company that was tasked with migrating data out of a CM system built by a company where I had also worked about 1

This, of course, isn't new. I once worked at a company that was tasked with migrating data out of a CM system built by a company where I had also worked about 10 years earlier. I ended up pinging one of the founders at the old company and asked him how we'd go about extracting the data using the platform's data (we were wondering because we kept running into stability issues doing this). He basically told me what I suspected, there was no good way to do that. Because of the way the cache worked in the product, it would never stay up if every single data record were fetched via the API. We ended up pulling it all out of the database directly, which was a bit of a pain. tl;dr no vendor really wants to make it easy to pull ALL of your data out of their system.