They both face the same problem, namely that the web and paper work completely differently and there are untranslatable concepts. So you have to define some way in which your typesetting gracefully settles into a different environment.
If typst had targeted html immediately it certainly would have made their life a lot easier, but it would have been nothing more than an overly complex site generator. Targeting PDF first means that they actually want to compete with LaTeX.
PDFs are a digital recreation of paper documents, with all the drawbacks of that.
Targeting ePub is essentially the same as targeting the web, the distinction between having the file locally or retrieving it from a server seems entirely meaningless in this context.
>not because I believe it is a good format.
It is a pretty much perfect format within the constraints.
They both face the same problem, namely that the web and paper work completely differently and there are untranslatable concepts. So you have to define some way in which your typesetting gracefully settles into a different environment.
If typst had targeted html immediately it certainly would have made their life a lot easier, but it would have been nothing more than an overly complex site generator. Targeting PDF first means that they actually want to compete with LaTeX.