Lately (last 10 years or so) these have tended to be acqui-hires, which is probably what Open AI was doing, either to acquire people with specific skills and subject matter expertise, or to deny it to your rivals.

Not sure about this specific instance, but there are other useful artifacts in open source companies too, since they usually have an enterprise support, hosting and/or gated premium feature upsell business model. This means they have customer data such as usage patterns, contact info of purchasing decision-makers, and technical points of contact in other businesses plus sometimes a cache of UGC from their hosted offerings. Keep the hosted offering running for a bit after acquisition and throw in a sly change of the user agreement and it’s all yours for the taking.