Specialization is at the heart of increasing productivity. Let's say a given person makes awesome travel videos. If that person can find a way to broadcast and monetize those videos with YouTube, Vimeo, or whatever, that almost certainly makes more sense than devoting their time to maintaining their own streaming platform. That's time the person could have spent continuing to refine their actual product: travel videos.
Video editing and production are extremely time intensive tasks that require a lot of skill; people work on these skills their whole lives. Likewise, dev ops and infrastructure management are incredibly deep rabbit holes to jump down. The idea that every hobbyist blogger, photographer, and indie band should learn about server administration seems crazy to me.
Does not owning your platform have risks? Of course. Everything has risks and business is always about tradeoffs. Platforms like YouTube solve a lot of problems for content creators. For most creators, those benefits are going to outweigh the costs.