The goal was always that the user would be the product. It was less clear at the beginning, because the advertising was far less intrusive (if you even saw an ad at all, in the early days), and the service was “free” at a time when the internet was comparatively young. So it gained a lot of popularity from novelty and being an actually useful communication tool.
But the communication tool portion was always a side effect of data collection. Any “free” service is ultimately just getting value from you in different ways. In the case of Facebook, once it had amalgamated enough data, the flood gates opened and the enshittification was extremely rapid. It will never go back to the way it was for many reasons, not the least of which being: it was designed to be the cesspool it is now.
Ultimately, all these seemingly random posts are an attempt to get you to continue to interact with the platform. If you read through comments on such posts, they do tend to drive engagement, even if it is just a user going “why is this in my feed?”