I follow over 1000 creators on YouTube, many of them niche creators who don’t often upload content. There are a very small percentage who are on another platform.
The main app that I use (Tubular) also supports PeerTube, but PeerTube has a big issue when it comes to both content discovery and delivery. YouTube hosts not only the “full” quality video, but they also host many different versions of the same video at varying resolutions/bitrates. This is unfeasable for basically anyone but a big tech company. YouTube also has a very effective (albeit very flawed) recommendation algorithm that smaller platforms struggle to compete against.