PDF is optimized for printing paged media. When I read (instead of skim) physics and math papers I still prefer to print them out. Pagination support is still very primitive in the web stack, at least when I last tried https://www.pagedmedia.org/paged-js/. EPUBs are good until you have equation blocks, floats, etc., then they are pretty far TeX/LaTeX-level typesetting.