I don't understand why no other video platform has broken into YouTube's market share, after the last couple years' constant stream of PR disasters which mostly have to do with the scale of the platform
If users are on YT, that is where the content creators will be. And if the content creators are on YT, that is where the users are. Moreover, users have curated lists of subscriptions and creators have large lists of material. Finally, YT has access to a lot of data on viewing behavior, and likes. This means YT should be a lot better at recommending videos to users.
Finally, the creators that most want to switch to an alternative are those who are the most censored. These tend to be more controversial, which means these alternative services gather controversial content. This tends to give these places a bad reputation which pushes away the non-controversial content.
The best bet would probably to take a non-controversial niche, start there, and try and integrate well with YT to keep down switching costs. Its still hard to provide actual added value to such a niche. Alternatively one might take a controversial niche with wide acceptance. For example, gun channels or LGBTQ+ channels. Both are currently demonetized, but both are still widely accepted in broad swathes of society.
this is hardly the case, as any avid youtube watcher can tell you. Recently, the algorithmic suggestions are terrible, and either show repeated content, or content that's not even close to what's being watched (but the SEO/words in the description/title matches), or is a huge list of videos from the same channel.
Facebook only has network effects, there isn't anything particularly efficient or advanced about what it does. Given its minuscule infrastructure when compared to Google and Amazon, it would be very hard for it to achieve the same level of cost that Google has on YT. Pure search doesn't rely so much on scale as well.
Any other provider doesn't have either the network effects that YT does nor the scale to be able to compete with Google on YT.
From a scale perspective, the only companies who could effectively compete with Google would be Microsoft and Amazon. Microsoft is still trying to figure itself out, especially on the consumer side. Amazon is geographically limited and has very little expertise in open content and ad-funded platforms, but it is trying with Twitch.