The gp (notatoad) mentioned technical skill as a barrier and you responded to that point but easy-to-use idiot-proof software isn't really the issue.
The bigger problem(s) mega-sites like Youtube solves is financial.
When one uploads a video to Youtube, it doesn't matter if it gets 0 views or 1 billion views. The cost is the same to the uploader: $0. Hosting it on one's own with AWS/Azure/GCP/DigitalOcean/etc will have variable egress costs and budgeting/forecasting a potential expense of thousands of dollars is not something regular people want to tackle. (The difficulty of this should be apparent from the stories of sophisticated tech geeks getting blindsided by unexpected AWS bandwidth bills.) The other option of placing a bandwidth limit to cap the costs means you create a different problem: a popular video will result in web surfers seeing annoying "bandwidth exceeded" error messages.
Another financial problem Youtube addresses is monetization. Hosting it on a self-managed cloud means less opportunities for ad revenue. Yes, a lot of HN despise ads but many uploaders of desirable video content like the ad payouts.