The competitors have a hard time gaining traction because in the way many of us would expect because we live in a different world from when YouTube first became a thing.
YouTube in 2005 was way different. You could find just about anything on there. Pranks, home videos, entire TV shows, bumfights, skits, you name it. Mostly young people used it, and back then the youth were a little more "based" than my impression of Gen Z today. I remember older folks like my parents almost universally dismissing YouTube as "a bunch of crap" and how wrong I felt they were. Guess who turned out to be right about the future of information and entertainment!
Today, I'd wager everyone's interacted with YouTube at least once. There is nothing edgy or fringe about YouTube anymore. It's a mainstream media platform saddled with its past that it just can't shake. Without big advertisers and big audiences, it wouldn't be sustainable, thus it has developed to not offend the normies or their political allies.
Many have moved over to other platforms, but they are essentially the same kind of audience and creators that were on YouTube back in the old days. The so-called normies who didn't take YouTube seriously back then are now easily frightened of the dangerous content found on alt-tech. They are unlikely to ever move away from the warm fuzzy feeling only provided by the MSM and Silicon Valley.
Although I desire people be a little less allergic to supposedly dangerous content, can we really blame people for being disinterested or avoidant to YouTube competitors?
Maybe this is the way it should be. Average Joes/Janes/Jaydens will be happy on YouTube and TikTok, and the ends of the bell curve will find their place on smaller platforms that aren't interested in pleasing everyone.