Why does everyone need to be a convert? I'm not even sure that anyone needs to be a "convert" for it to succeed. e.g. MIT OCW uses youtube as its main host right now, which is not a great fit for CC BY-NC-SA material (ads + difficult downloading directly contradict that license). They could run a peertube instance to make it easy for users to exercise their rights while still posting it to youtube for reach. Or similar to how the mathematics community has moved from Twitter to Mathstodon, they could run a peertube instance for lectures, lean conference talks, etc.
Joe Schmoe doesn't need to know what peertube even is. Whoever is going to set it up for an organization/community does. If Joe is in such a community, finding their instance works the same as finding their youtube channel: you link to it. Actually it works better because by nature of being small and focused, the instance lets you easily discover related channels or make your own and have it discoverable by the community. Youtube discoverability is actually kind of trash by comparison, and relies on search (which requires you to know what you want already) or popularity/"the algorithm" for recommendations.
Since Joe doesn't need to know what it is, they don't market to Joe. They talk to community managers and IT people, e.g. on their front page:
> PeerTube is a tool that you install on a web server. It allows you to create a video hosting website, so create your "homemade YouTube".
It's never going to achieve "success" in the sense that the latest Mr Beast or Megan Thee Stallion video is there, but that's okay. Those aren't the target audience.