Mithril has a detailed “why this instead of react/vue/etc” article https://mithril.js.org/framework-comparison.html that I think should be mandatory for any library entering a crowded space like this. If only because i want to know the priorities of the developers.
That would be nice, but also we observers are not owed any such explanation by the creator.
No, but communities can set expectations, and then someone can choose to meet or buck the expectations of the community at their own risk.
A good example of this is the TodoMVC convention. Instead of making "whatever demo app you choose" a convention developed to make a Todo app, so that people could compare frameworks in a more "apples-to-apples" way. A new framework with a Todo demo would likely get more traction than a framework with a Calendar demo, because it's easier to evaluate and understand how it works.