I think that these companies are understanding that as the barrier to entry to build a frontend gets lower and lower, APIs will become the real moat. If you move away from their UI they will lose ad revenue, viewer stats, in short the ability to optimize how to harness your full attention. It would be great to have some stats on hand and see if and how much active API user has increased decreased in the last two years, as I would not be surprised if it had increased at a much faster pace than in the past.