Nothing at all. I'm not making a value judgment on Youtube Premium. I'm saying it's not the same class of service as Quibi and thus not a counter-example for how Quibi could/should have succeeded. They're fundamentally different things with completely different non-user to paying customer paths. Quibi wasn't Youtube. Quibi is 2013 Netflix if it didn't have any non-original content. Except 2013 Netflix wasn't dumb enough to charge you money and still show you ads.
What? Most video content is exclusive to a single platform already? If you think HBO, Disney+, Netflix originals, etc., are too expensive, you don't have other options there either in paying less from someone else. Why should you expect to be able to do so??
If anything YouTube is the most open platform by far, because the vast majority of the content on there is owned by the creators, not YouTube, and thus it could be on other platforms, in a way that will never happen with the paid streaming services. Indeed this is even happening with CuriosityStream.