I suspect they are building their B2C products because it gives them better data to train on. It's a lot harder to control the quality of data when you have no idea how API inputs were produced, what the UI is like, or who the users are. You don't know the provenance of the data, or the context. Or even if multiple unrelated client products are being commingled through the same key.

If you control the UI, you have none of those problems.