TikTok is the most prominent one, for a number of reasons, but other platforms that pioneered or copied the format also reached considerable prominence. Instagram Reels, Snapchat Stories, etc. And tellingly, when YouTube wanted to compete, they needed to build an experience quite separate from the rest of the site. There is a qualitative difference in how people perceive and consume this type of content. It's not just "vertical YouTube".

Of course each one of these platforms was backed by VC or stock market money, but that's the nature of the industry. Over the years, VCs ended up throwing a lot of money at Google and YouTube killers and that didn't get them anywhere, so that in itself isn't the winning formula.